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Glossary
Company code with its associated company name
AFW | Affinity Water
ALE | Albion Eco Ltd
ALB | Albion Water Ltd
ANH | Anglian Water Services Ltd
BRL | Bristol Water Plc
CAM | Cambridge Water Company Plc
DWR | Dŵr Cymru Welsh Water
ESP | ESP Water Limited
HDC | Hafren Dyfrdwy
ICW | Icosa Water Ltd
IWN | Independent Water Networks
ISC | Isles of Scilly
LNW | Leep Networks Water
NES | Northumbrian, Essex and Suffolk Water
PRT | Portsmouth Water Plc
SES | SES Water
SVT | Severn Trent Water Ltd
SEW | South East Water Plc
SST | South Staffordshire Water Plc
SWB | South West and Bournemouth Water
SRN | Southern Water Services Ltd
TMS | Thames Water Utilities Ltd
UUT | United Utilities Water Plc
VWP | Veolia Water Projects
WSX | Wessex Water Services Ltd
YKS | Yorkshire Water Services Ltd
Foreword
Dedication
The Chief Inspectors Report 2024 is dedicated to the memory of Suzanne Calmels. Suzanne passed away in April 2025 after working for the DWI for more than 20 years. Her incredible organisational skills and attention to detail has benefitted water quality in England and Wales for millions of people.
Figure 1 – Suzanne Calmels
The provision of clean drinking water is fundamental to the health and wellbeing of society and economic prosperity, and access to clean water is a basic human right recognised by the United Nations. The advances in water safety planning and systems management underpinned by robust water quality regulation provide some of the best drinking water in the world. Drinking water quality in England remains excellent, with public supplies consistently meeting the stringent regulatory standards for drinking water. Compliance with the standards in 2024 was 99.97%, although the challenge remains to achieve 100% compliance with the regulatory standards.
Drinking water supplies in England are protected by water safety planning which provides a robust multi-barrier approach. In this process, risks are identified from source to tap, and mitigation put in place to address the risks before there is any deterioration or impact on consumers. The quality of supplies is further verified through extensive random sampling. Occasionally things go wrong, and when this occurs, the Inspectorate investigates, assesses compliance breaches and events, and takes enforcement action to prevent recurrence. Summary details of the regulatory activity carried out by the Inspectorate during 2024 are presented in this report, and further details of company improvement programmes are published on the Inspectorate’s website.
Our water supply system is under pressure from a range of different threats, and these are made more urgent by climate change and population growth. In January, I made recommendations to Ministers for updates to our regulations including drinking water quality, sufficiency, and alternative sources such as recycling.
The recommendations for drinking water have formed the basis of guidance to water companies, with the ultimate objective to update the regulations to meet modern standards of quality. This will enable consumers to remain confident in the quality of their drinking water, and that they are protected from exposure to contaminants.
Resilience of supplies, security, sufficiency in times of drought, and safe water recycling schemes and new and new and innovative treatment processes to secure continuous supplies which all users can have confidence in. This purposeful strategy sets the foundation of delivering guidance based upon expert evidence for which future regulation may be delivered.
Nevertheless, legacy issues such as lead pipes and nickel in domestic dwellings, PFAS and other environmental threats as well as our infrastructure, security and operational technology are critical issues which need to be addressed. The Inspectorate has worked closely with OFWAT through the five-yearly price review to ensure there is adequate investment in these areas, but much remains to be done to improve asset health and resilience.
The government has launched an independent commission into the water industry, to reset the relationship between consumers, water companies, and the environment. This is an opportunity to think ahead and develop sustainable solutions which will meet the challenges facing the sector. I welcome this review and look forward to working with renewed energy and purpose to protect and improve drinking water supplies today and for future generations.
Marcus Rink
Chief Inspector of Drinking Water
Introduction
Drinking Water 2024 is the annual publication of the Chief Inspector of Drinking Water for England and Wales. It is the 35th report of the work of the Inspectorate and presents the summary information about drinking water quality for the calendar year of 2024. It is published as a series of four quarterly reports and a final summary report, which covers public water supplies, and a single report, which covers private water supplies. This report is the summary of public water supplies for England. The industry dashboard for England 2024 is shown in summary below:
Figure 2 and table 1 – Industry overview
Compliance
Parameter Group
% Compliance
Chemical Parameters
99.95%
Indicator Parameters
99.97%
Micro-Biological Parameters
99.98%
Micro-Biological Parameters (Reservoirs)
99.96%
Micro-Biological Parameters (Treatment Works)
99.98%
Pesticides
100%
Overall
99.97%
Events
Events – Not an event
9
Events – Not significant1
165
Events – Minor
197
Events – Significant
137
Events – Serious
18
Events – Major
1
Median compliance risk index
2024
1.741
2023
3.02
Consumer compliance on acceptability contacts per 1000 population
England
1.21
Industry average
1.3
Risk assessment risk index
Industry median RARI
7.78
Enforcement
Recommendations
836
Legal instruments served
201
Companies in transformation
6
Water supplies and testing
Set out in this report are the key facts about the quality of the public water supplies in England, which is served by 25 water companies delivering supplies to nearly 59 million consumers.
Key facts
Public supply key fact
Statistics
Number of water companies
25
Population supplied
58,819,999
Water supplied (L/day)
13,925,522,000
Treatment works
998
Service reservoirs
3,632
Water supply zones
1,917
Length of mains pipe (km)
321,866
Surface sources
1,144
Groundwater sources
1,009
Mixed water sources
347
Table 2 – Compilation of data from all water companies
Key facts for private water supplies
Private supply key fact
Statistics
Population supplied
849,800
Water supplied (M3/day)
745,167
Number of supplies
34,859
Number of local authorities with private supplies
207
Sources without a risk assessment
22,611
Table 3 – Compilation of data from all local authorities
Figure 3 – Water companies in England and Wales
Inset appointments
Company
Zones
Volume supplied (l/day)
Population
ALB
3
698,000
3,000
ALE
1
33,000
180
ESP
22
482,000
3,855
ICW
66
3,982,000
24,886
IWN
166
27,625,000
221,000
LNW
63
12,085,000
93,500
MTX
1
74,000
435
MUA
3
0
5
VWP
1
5,900,000
17,604
Total
331
51,724,000
366,467
Table 4 – Key facts about inset appointment companies 2024 data
IWN is the first inset appointment company to exceed a total population of two hundred thousand, these companies have traditionally been small and only import water from other incumbents for onward distribution, however reaching this milestone means that IWN is now comparable in size to a more mainstream incumbent company.
The number of samples taken by each water company is within Annex A.
Compliance with water quality standards
The percentage of compliance with the standards in the Water Supply (Water Quality) Regulations 2016 (as amended) is shown below, and details of all the failures are set out in Annex 3 by site type and by company.
Parameter group
% Compliance (2dp)
Chemical parameters
99.95%
Indicator parameters
99.97%
Microbiological parameters All
99.98%
Microbiological parameters (Reservoirs)
99.96%
Microbiological parameters (Treatment works)
99.98%
Pesticides
100.00%
Overall
99.97%
Table 6 – Overall compliance table
The diagram below represents the quality of drinking water received by consumers, and the numbers and parameters which failed to meet the standards in 2024.
Figure 5 and Table 7 – 2024 compliance overview
Parameter name
Number of failures
Coliform bacteria (zone)
344
Coliform bacteria (WTW & SR)
202
Iron
82
Nickel
70
Odour
68
Taste
56
Lead
53
E. coli
40
Turbidity (WTW)
19
Aluminium
18
Manganese
11
Radon
11
Clostridium Perfringens
8
Colony counts after 3 days at 22°c
8
Enterococci
8
Chloride
7
Copper
5
Turbidity (zone)
5
Pesticides Propyzamide
3
pH
3
Bentazone
2
Benzo[a]Pyrene
2
Ammonium
1
Free chlorine
1
Nitrite
1
PAH
1
Pesticides Aldrin
1
Pesticides Dieldrin
1
Sodium
1
Total chlorine
1
Total
1033
Compliance with the drinking water standards is consistently high in England. Testing is designed to verify drinking water quality at practicable intervals at key supply system locations. However, scrutinising company water safety plans, audits and events reveal risks within drinking water supply systems which on investigation may require additional mitigation to reduce risks.
The Inspectorate has developed a series of risk indices to identify where companies should address risks to supplies. It uses the Compliance Risk Index (CRI) to measure the impact of a compliance failure on company performance, and the potential impact of those compliance failures on consumers. CRI is designed primarily for the purposes of effective regulation, ensuring appropriate scrutiny is directed to those areas of greatest relative risk. The bar chart below shows the CRI for each company operating in England divided into site types, zones (consumer taps), water treatment works and service reservoirs.
Of all the compliance failures during 2024, 472 were related to consumer distribution systems.
CRI by company
The CRI is not a statutory measure; it does not remove the duty for a company to comply with each parametric value set out in the Regulations. However, as a risk-based metric, the objective is to incentivise the companies resource to focus on highest risk in a precautionary manner. It is shared with the financial regulator, Ofwat, as a common performance measure as an integrated regulatory strategy intended to promote improving water quality in the public interest. Whilst the Inspectorate does not accept any compliance failures as being acceptable, a CRI target of 2 has been set as the point from which financial penalties apply, ensuring outcomes remain risk focused, achievable and equitable when used as a water quality performance objective.
The median value for the industry in2024 is 1.741 which reflects a change in risk-focus through regulatory activity when compared to 3.040 in 2023, 1.365 in 2022 and 1.171 in 2021. The interpretation of the median CRI for the industry can be complex because it combines two factors; the performance of companies and the regulatory action taken by the Inspectorate, since the issuing of notices in response to risk purposefully augments the measure creating a focus on areas of greatest need. Those companies in the top half reflect the ongoing strategic risks and the consequent increase in regulatory action. The overall CRI is comprised of figures representing performance of different parts of the water supply chain (treatment works, supply points, service reservoirs and zones). The data includes all regulatory failures, such as indicator parameters taken at treatment works, service reservoirs and consumer taps, and is used for the CRI calculation. The objective is to highlight all risks and all locations which require improvement.
Failures at water treatment works contribute the greatest amount to company CRI scores. They score highly because of the large population served reflecting the relative risk to the largest number of people. These sites are wholly within the companies’ control meaning that failures should be adequately mitigated and avoided.
Figure 6 and Table 8 – Company compliance risk index scores
Code
Reservoirs
Supply Points
Treatment Works
Zones
Total
Eng_CRI
Deadband
ISC
1.14
3.71
18.37
1.52
24.73
5.24
2
NES
0.20
0.00
8.60
2.14
10.94
5.24
2
SVT
0.08
0.02
9.19
1.02
10.32
5.24
2
UUT
0.26
0.27
7.79
1.96
10.28
5.24
2
SST
0.02
0.00
7.31
0.57
7.90
5.24
2
ALB
0.00
0.00
0.00
5.20
5.20
5.24
2
SRN
0.03
0.00
2.00
1.78
3.82
5.24
2
YKS
0.23
0.00
2.12
1.26
3.61
5.24
2
BRL
0.46
0.16
0.65
1.57
2.84
5.24
2
LNW
0.00
0.00
0.00
2.13
2.13
5.24
2
ANH
0.45
0.00
0.77
0.89
2.11
5.24
2
TMS
0.34
0.23
0.77
0.70
2.04
5.24
2
CAM
1.06
0.00
0.39
0.00
1.45
5.24
2
AFW
0.77
0.00
0.00
0.67
1.44
5.24
2
WSX
0.13
0.00
0.54
0.63
1.31
5.24
2
SWB
0.08
0.00
0.69
0.42
1.19
5.24
2
SEW
0.29
0.00
0.03
0.77
1.09
5.24
2
PRT
0.00
0.00
0.45
0.00
0.45
5.24
2
IWN
0.00
0.00
0.00
0.32
0.32
5.24
2
ESP
0.00
0.00
0.00
0.21
0.21
5.24
2
ICW
0.00
0.00
0.00
0.15
0.15
5.24
2
SES
0.00
0.00
0.00
0.00
0.00
5.24
2
The highest scoring parameter by a considerable majority is total coliforms which accounts for over half of the total CRI score on its own.
Table 10 – Microbiological failures at treatment works in 2024
Microbiological failures
E. coli
The detection of E.coli indicates faecal contamination and robust contingency plans must be in place to mitigate the impact of detections and provide protection, for the public, from water which may be considered unwholesome and potentially unfit. Throughout 2024 there was only three detections of E. coli in samples taken from treatment works from 171,591 tests carried out, from service reservoirs there were seven detections from 182,653 tests and from consumer properties there were 30 detections from 153,474 tests carried out. In total there were 40 E. coli detections in 2024, this is an improvement over the 41 in 2023.
Southern Water – Stanhope Lodge Worthing WTW – E. coli
In June 2024, three E. coli and 67 coliforms were detected at Southern Water’s Stanhope Lodge treatment works. The detection was also reported as a drinking water quality event. Stanhope Lodge is under notice SRN-3926 which covers risks associated with ingress/treatment failures leading to bacteriological detections. The company investigation did not identify any issues with structural integrity and did not identify any deficiencies with the operation of the disinfection system which is provided by UV. Pre and post UV samples taken on the same day that the failing sample was collected were clear of bacterial detections.
Resamples were taken from the compliance point as well as a downstream service reservoir and consumer properties, which all returned clear. A site inspection did identify that some improvements were needed such as the removal of the redundant gas injection lines and old main dose instrument sample line, capping of the Quadrina tapping and sealing of ducts in chambers. There had been no E. coli detected in the raw water in the lead up to the detection or in the previous three years.
The company conclusion was that the most likely cause was contamination of the sample. However, in the absence of any evidence to support this conclusion the company undertook enhanced monitoring for three months with no further detections reported. The company confirmed to the Inspectorate that the improvements identified during the site inspection had been completed onsite.
Anglian Water – Little Melton WTW – E. coli
Seven E. coli were found in a regulatory monitoring sample collected from the Anglian Water Little Melton treatment works on 09 April. Investigations found ingress into a reservoir at the works and remedial work to repair was undertaken.
Following a later repeat coliform detection in a sample collected on 16 June, the company installed temporary ultra-violet (UV) treatment.
The sampling investigation undertaken by the company for the second failure was inadequate with only one consumer sample taken, despite the works supplying a large population. Recommendations were made by the Inspectorate to re-brief teams responsible for arranging resampling surveys to ensure an appropriate investigation is undertaken to ensure that public health is not at risk.
Thames Water – Horton Kirby WTW – E. coli
In January 2024, E.coli was detected in a sample from Thames Water’s Horton Kirby works. Despite heavy rainfall at the time of the exceedance, the company’s investigation concluded that there had been no ingress to the treatment process.
However, the investigation reported that the sample tap at Horton Kirby is kept running continuously and that therefore the flame sterilisation of the tap, with the water running is poor practice. The company subsequently changed their sampling procedures to allow taps to be disinfected whilst running. The Inspectorate shall take further action to address this issue across the company to ensure that sampling procedures are in line with industry good practice and that samples are representative.
Coliforms
Testing for coliform bacteria gives reassurance that water entering supply was treated adequately to remove bacterial and viral pathogens. Repeated occurrences of coliform bacteria in samples from the same works in one year are thus of concern and require action to be taken. There were 80 coliform failures from 171,598 tests undertaken.
Equally, testing for coliform bacteria gives reassurance that the quality of water held in service reservoirs at strategic points in the distribution system is adequately maintained. The national standard requires that at least 95% of no less than 50 samples collected from each service reservoir throughout one year are clear of coliforms. From the 122 failures from 182,652 tests for coliform bacteria four reservoirs failed the 95% rule. Of these reservoirs Mynd and Chillies were not in service for the whole year and were taken out of service following the failures.
Severn Trent Braybrook reservoir was removed from service one cell at a time and ingress was identified and repaired in both cells.
Company
Site name
Parameter
Samples taken
Samples failed
Percentage compliance (2 DP)
SEW
Chillies Reservoir Outlet 1
Total coliforms (confirmed)
1
1
0%
SVT
Mynd DSR
Total coliforms (confirmed)
9
1
89.89%
SVT
Braybrook DSR combined Outlet
Total coliforms (confirmed)
52
3
94.23%
YKS
Oughtershaw SRE
Total coliforms (confirmed)
52
6
88.46%
Table 11 – Service reservoir wholesomeness test
Yorkshire water – Oughtershaw reservoir – Coliform bacteria
A compliance sample taken from Oughtershaw service reservoir on 24 September 2024 was found to contain 122 coliform bacteria per 100ml. On 25 September 2024, a restriction of use boil water advice was provided to one property downstream of the asset in the K848 Oughtershaw district metered area in North Yorkshire and on 26 September 2024 boil water advice was provided to the remaining eight properties. In total, Oughtershaw service reservoir breached schedule 1 of the Regulations once for E.coli and six times for coliforms in 2024. Oughtershaw service reservoir was not fully bypassed and taken out of service until 4 March 2025. Microbiological water quality improved significantly thereafter, and the health protection advice was lifted at all properties on 13 March 2025. Restriction of use advice remained in place for consumers for 201 days.
Although the company’s investigation carried out extensive sampling surveys and found an NRV that was causing depressurisation in the inlet main early into the investigation, it was not until 9 December 2024 that the company carried out a walkover of the main and discovered an unmapped air valve. Satisfactory sample results were interspersed with detections of indicator organisms and therefore, the inconsistency in the company’s sample results further led to a delay between interventions carried out. The company’s investigation would have benefited from a more robust application of procedures, processes, and root cause analysis to fully assess the potential risks associated with both existing and legacy infrastructure.
The Inspectorate recommended that the company review its procedures to ensure investigations are initiated and carried out promptly, in order to mitigate the risk of future regulatory breaches. In addition, suggestions were made for the company to review its asset records to support effective incident management and ensure that system-wide learning is captured and applied following this event.
The public health implications from this lack of reservoir inspections and lack of records for their air valves could have been severe and in this instance the company were lucky and got away with it.
The company plan to create a new Continuous Improvement team which will be tasked with investigating the root cause of water quality failures. The company also has a “red-lining” process by which asset records will be updated as and when a physical discrepancy is discovered in the network or other Company assets. Companies should take learning from this event to ensure that investigations are initiated early on to prevent prolonged risks to public health and extended consumer disruption. Prompt root cause analysis and asset assessment must be standard when microbial breaches occur and robust processes are needed to assess risks associated with legacy infrastructure.
Severn Trent Water – Strensham WTW – Coliform bacteria
The compliance samples from Severn Trent Waters Strensham treatment works reported one coliform per 100 ml on 27 and 28 Feb, with three coliforms per 100 ml also reported for 2 March. Operational samples prior to the detection reported two post-disinfection samples which contained one coliform per litre.
The company concluded the operation of the treatment works to be satisfactory prior to exceedance, compliance with disinfection criteria had been maintained throughout. No changes in raw water quality had been observed. There was a potential concern identified in an ROV inspection of the north balance tank. However, the tank subsequently passed the flood test, which looks for signs of active ingress.
A potential ingress risk was identified in the high lift pump sump tank due to a leak on a pumped main within the pumphouse building causing water to collect in the cavity space of the sump tank wall. The leak was repaired on 13 March with the potential ingress risk also removed, however there were a further six post-disinfection detections between 13 and 25 March of one coliform per litre.
United Utilities – Oswestry WTW – Coliform bacteria
38 coliforms in 100ml were detected in a sample from United Utilities Oswestry treatment works on 16 August 2024.
The company had been carrying out significant valving operations between the 13 and 15 August 2024 to allow the installation of outlet pipework on the new rapid gravity filters. The work involved opening a valve that has been closed since 2020, which splits the slow sand filters into two streams. The company had written an appropriate method statement and undertaken a risk assessment for the work to demonstrate that a calm networks approach was implemented, and additional turbidity monitoring was put in place.
In addition to valving, the work also necessitated diverting the entire works flow via stream one, which involved closing the outlets on the stream two slow sand filters and bringing them back online via stream one. Three slow sand filters were returned to service, via stream one. After the coliform exceedance was reported to the company, a defect was identified with one of the slow sand filters. The filter was removed from supply and an investigation revealed that a tile on the filter floor had moved out of place, this would have allowed water to bypass the treatment stage. This was subsequently rectified and returned to supply. The company concluded that this could not be ruled out as the cause of the coliform detection.
Trends provided by the company further revealed that although the company could demonstrate the chlorine contact time was satisfactory and that water had been adequately disinfected prior to and on the day of the exceedance, trends from the stream one UV reactors show that there were outages on the system between 09:30 to 09:55 and 10:35 to 10:45 where no UV disinfection would have been occurring. Follow up information from the company confirmed that between May and October 2024, there were UV outages on 22 occasions at Oswestry works. The disinfection policy states that the UV dose is precautionary, however, because the UV reactors were installed to provide inactivation of Cryptosporidium, the Inspectorate concluded that regulation 26 applied to this process, therefore, failure of this system cannot be ruled out as the cause of the coliform detection.
The Inspectorate concluded that the company had not complied with the requirement to optimise existing treatment processes to ensure continuous compliance and had not satisfactorily implemented the requirement to complete the installation and commissioning of validated UV disinfection treatment capable of treating full works flow in notice UUT-2020-00003. The installed systems were capable of significantly reducing the bacteria risk buy by operating the system in the manner they did the company were not complying with the regulations which are in place to protect public health.
As a result, the company were issued with a regulation 28(6) intention to vary a notice and a further recommendation to review the trigger response times for UV outages to ensure that UV dosage was maintained at Oswestry.
Cambridge Water – Bluntisham Reservoir – Coliform Bacteria
Coliform detection at Bluntisham Reservoir 2. No root cause was identified, however the company have not yet completed the inspection and flood test of the reservoir, or the sample line audit. The company took the reservoir cell out of service to investigate on the same day the result was reported, and any required remedial works identified during the inspections will be completed prior to returning the reservoir to supply. Recommendations made regarding compliance sampling at the reservoir and the implementation of the company’s reservoir inspection program.
Affinity Water – Harefield reservoir 3 West – Coliform bacteria
A sample collected from Harefield Reservoir 3 West recorded a coliform bacteria result of 1/100mL in a sample collected on 19 March 2024. The company determined that the cause of the original failure was lower than normal turnover within the reservoir due to an increase in the water storage level. The company increased the reservoir water level as a precautionary measure should there be mains damage from HS2 work in the vicinity of another company main. The company was aware of the water quality risks associated with increasing water levels in the reservoir and subsequently reducing turnover.
This reservoir recorded five previous coliform detections in 2017-18. To satisfy the recommendation made in 2018 concerning turnover, the company operated the reservoir between 2018-2023 with either the East or the West cell in supply.
The company must consider and mitigate all risks associated with the supply of water – covering both sufficiency and quality matters. The company knowingly increased the risk of coliform detection at this reservoir by increasing the water level without the introduction of some appropriate mitigation. Indeed, the company determined that the cause of the coliform bacteria detection was lower than normal turnover due to the increased water storage level. It is not appropriate for a company to take actions and decisions that increase the likelihood of a coliform detection at any of its assets.
The risk assessment reports do not include turnover or water age as being hazardous events. The Inspectorate has now recommended turnover is a hazardous event and the risk assessment is resubmitted to the Inspectorate.
The company had a capital project for resilience to install booster pumps at this site to improve turnover. The project was due to be operational by August 2024. The capital scheme was completed and commissioned in February 2025 and the booster pumps are in use. The pumps are not yet operating at full capacity, and the company has kept one of the two reservoirs out of supply to ensure adequate turnover.
Turbidity
Turbidity is a measure of how much light can pass through water and indicates the cloudiness of water. Turbidity maybe caused by either inorganic or organic particles suspended in the water. At a treatment works, turbidity is an important critical control in relation to determining whether raw water has been adequately prepared for disinfection. The turbidity standard at treatment works is 1NTU. There were 19 failures of this standard from 171,438 tests performed in England. Two of the key failures are reported on below:
South Staffs Water – Seedy Mill WTW – Turbidity
Resamples collected in response to the turbidity failure at Seedy Mill works were satisfactory. The original sample was found to contain elevated levels of iron, manganese and aluminium. The treatment works had been operating satisfactorily and there had been no identified issues with sample collection or the laboratory analysis.
Black particles were observed in net samples placed over the tap on the final water compliance point, which were composed of higher-than-normal levels of iron, manganese and aluminium.
Further investigations identified the turbidity breach to be related to enabling works (valve operations) to isolate the North and South pre-suction and suction tanks, which were due for their internal inspections.
Northumbrian, Essex & Suffolk water – Lartington WTW – Turbidity
A regulatory sample taken from Lartington treatment works final water sample point returned a turbidity of 1.3 NTU. Further analysis of this sample returned an iron concentration of 890 µg/L, and an aluminium concentration of 430 µg/L, and also elevated concentrations of copper (95 µg/L). Resamples and related samples were taken from downstream service reservoirs which returned satisfactory results. The following weekly regulatory sample returned a turbidity result of >0.2 NTU and did not contain elevated concentrations of iron or aluminium. An audit was carried out on the regulatory sample tap and found that the connection onto the outlet main would draw water from the outside of the main, not the centre.
On 3 January 2024 the works experienced multiple communication issues with outstations. Ferric coagulant dosing was put into manual to ensure continuous dosing, however when the ferric pumps switched over, the standby pump started up at a higher pump speed. The resulting overdosing of ferric caused a peak over 100 mg/L of iron in the final water, the pre contact tank turbidity reached 0.3 NTU.
A recommendation was against the sample point, requiring a review of all works final sample points following exceedances at Wooler, Mosswood and Lartington treatment works. Condition of sample points causing compliance failures is a recurring issue within the water industry and something that is completely within the control of the water companies to affect certainly given the financial implications of failures as they affect the CRI scores.
Chemical failures
The table below shows all the chemical failures during 2024, the full list of all chemical parameters sampled in included within annex B.
Parameter name
Standard
Total number of tests
Tests not meeting the standard
Tests not meeting the standard per company
Percentage compliance (3 DP)
Benzo[a]Pyrene (total)
0.01 µg/L
13,174
2
TMS(1) IWN(1)
99.985%
Polycyclic aromatic hydrocarbons (total by calculation)
Table 12 – chemical parameter sample numbers and number of failures
From samples in zones, iron, manganese and aluminium contribute 29% of all the chemical failures. This emphasises the impact the potential causes of discolouration that can affect consumers. Iron and aluminium are the two base chemicals used in the treatment of surface water during the primary coagulation stage. They are of high importance as part of a multi barrier approach to treatment as they remove the bulk of particulate matter from water, however their use should be tightly controlled to ensure that no excessive carryover of either chemical occurs. Should this occur then the company risks ‘seeding’ their distribution network with particles which can build up over time and should any rapid flow changes occur then this could result in a downstream discolouration affecting a large number of consumers.
Taste & Odour
Albion water – Rissington – Taste
In July 2024 an Albion water sample from one of their zones reported positive for a taste result. The company concluded this was associated with the consumers tap. However, upon investigation by the Inspectorate it was found that the company had not conducted any investigation into the breach.
No investigational samples were collected, a fittings inspection was not carried out, upstream assets were not investigated and inappropriate advice was provided to the consumer.
The Inspectorate has taken this lack of action by the company very seriously and has raised recommendations regarding procedures, investigations, and provision of information. A follow up meeting with the company also took place to discuss expectations around reporting, investigation and safeguarding public health.
Nickel
High concentrations of nickel in tap water can cause skin irritation (allergic contact dermatitis). Nickel represents 18% of all chemical failures, this is primarily a consumer distribution system issue and commonly associated with newly installed taps which can be seen by the high number of failures from the inset companies IWN (5), LNW (2) and ESP (11) relative to their population size. Nickel may be present in coatings on modern tap fittings which are widely available, so can occasionally leach into water whilst it in contact with the fitting and are often the cause of failures in this area.
Advice should be offered by companies to consumers where these failures occur and consumers can help themselves by flushing their taps following any periods of stagnation. If you need to replace a tap or fitting, we recommend that you employ a qualified plumber to carry out any plumbing work. The Water Regulations Advisory Scheme provides information about accredited WaterSafe plumbers and approved fittings on its website.
Copper
Copper is in regular use throughout the country as a plumbing metal within the domestic, commercial and industrial sectors, the chemical properties of copper are excellent in this application as it is easy to use and has an inbuild level of microbial resistance. Failures of copper are rare, however the 5 exceedances in 2024 are noticeably higher that in other years.
Where failures do occur this is normally related to the installation of new pipework and/or low turnover. In many cases the copper was also associated with a high level of lead where pipework was identified as being galvanised. In those situations the company can undertake a water fittings inspection to identify if there are any issues, where the communication pipe is identified as being the cause the company is required to replace this
Sodium
Sodium failures are normally associated with water softener installations. Water softeners work by removing minerals like calcium and magnesium from your water supply through a process called ion exchange, effectively softening the water. This process involves using a resin bed coated with sodium ions. When hard water passes through the resin, the calcium and magnesium ions are attracted to the resin beads, while sodium ions are released into the water, thus softening it. Both calcium and magnesium are essential minerals and beneficial to human health in several respects. Inadequate intake of either nutrient can result in adverse health consequences.
A water company sampler should be checking with the consumer if a softening system is present, if there is a system they should avoid sampling from the softened tap as this is not representative of the mains supply. For the single failure which occurred for Affinity water, the sampler was directed to what was supposed to be an unsoftened tap
As far as consumers are concerned if you do install a water softener, it is very important that you make sure that it is correctly installed, and you do not soften the water to the tap in your kitchen which is used for drinking and cooking. This is because most water softeners work by replacing the hardness with sodium. Too much sodium can be a problem for premature babies because their kidneys are not good at filtering it out of the blood, and for people who are on a low sodium (low salt) diet. Artificially softened water may also be aggressive to plumbing causing leaching of copper and lead.
When purchasing a water softener, we advise that you buy it from a reputable supplier. It should be installed only by a qualified plumber who is a member of a recognised trade association, such as the Institute of Plumbing. We also advise that you consider putting in place a maintenance contract to ensure the softener continues to operate correctly and does not become a hygiene hazard.
Benzo (a) pyrene
Independent Water Networks Limited detected a Benzo (a) pyrene breach in its Tendring underground zone in January. Repeat samples at the property and investigation samples from neighbouring properties did not detect Benzo (a) pyrene above the limit of quantification. The company determined that the likely source was from the breakdown of coal tar lining of older cast iron mains within the bulk supply company network. The bulk supplier confirmed the presence of older mains upstream of the company’s water supply zone.
Fluoranthene was detected in all the samples collected as part of the investigation. Therefore, the Inspectorate did not concur with the company view that the failure is unlikely to recur.
The Inspectorate made recommendations associated with regard to the monitoring protocols the company had in place and failing to review the risk assessment for PAH related parameters in this zone in a timely manner
In July, there was an exceedance of the Benzo (a) pyrene standard in Thames Water’s Epping Forest zone, the cause was related to the temporary mobilisation of mains material as the result of a local burst main, investigatory results confirmed elevated PAH results nearby in the vicinity of the burst. There are coal-tar lined mains within the area and this risk had already been identified by the company and the Inspectorate had already issued a regulation 28 notice to address the risk. Following the repair of the main and the return to the usual supply arrangements within the area sample results returned below the regulatory standard.
Pesticide failures
Pesticide name
Standard
Total samples
Total failures
Comments
Aldrin
0.1 µg/L
3,732
1
LNW(1)
Propyzamide
0.1 µg/L
5,128
3
UUT(1) SVT(2)
Dieldrin
0.1 µg/L
4,329
1
LNW(1)
Bentazone
0.1 µg/L
5,294
2
TMS(2)
Total
18,483
7
Table 13 – Pesticide failures
During 2024 there were 7 failures for pesticides from 18,483 samples taken, the overall compliance rate to 3dp is 99.997%. Failures of the pesticide standard have reduced year-on-year since 2014 partly due to catchment management initiatives and the associated undertakings by companies as well as continuing improvements in treatment such as the use of granular activated carbon among other technologies.
Some pesticides, whilst not impossible to remove by treatment, are difficult, expensive and problematical with available technology. The strategy for companies has therefore been to work with stakeholders in the environment to promote catchment management and to improve source water. Source water is subject to even the smallest changes in the environment which can have a profound impact on drinking water and companies will need to remain vigilant in their respective areas .
Propyzamide
The United Utilities failure investigation concluded that the exceedance of 0.153µg/l was caused by the application of propyzamide to already saturated land adjacent to the River Dee, following which there was a period of heavy rain in early February 2024, that subsequently washed the propyzamide in to the River Dee. The company have put several actions in place to prevent a reoccurrence including established a working group to review propyzamide risk on the River Dee catchment, engaged with the main manufacturer of products that contain propyzamide for technical support and engaged with the landowner who advised they would not consider growing oil seed rape on the land for the next three years.
Severn Trent water had two failures from their Wolverhampton zone in 2024 in the areas supplied by the bulk import from South Staffs Water’s Hampton Loade WTW are a result of treatment deficiencies at the supplying treatment works. Upgrades to the treatment works in the near future will allow changes to the filtration at the works which should ensure more effective pesticide removal.
Aldrin and Dieldrin
Both of the failures from Leep networks water are associated with a laboratory problem and repeated AQC failures meaning that there was insufficient sample to fully complete the analysis, which resulted in the company’s contracted laboratory reporting a result with a raised LOD, which was higher than the PCV for these pesticides. The laboratory was unable to confirm the exact levels of the pesticides, only that it was <0.032µg/l for aldrin and <0.036 µg/l for dieldrin.
The company’s current process with requires any anomalies to be raised with the company’s contract manager, however the issues with the AQC failures resulting in insufficient sample were not reported to the company prior to the release of the analytical data. Further to this, as the results were reported with a less than ‘<’ which preceded the result, this did not flag on the system as a failure.
When the laboratory released these sample results to the company, commentary relating to the AQC failures was added to the analytical report however these were not identified by the company. As such, the sample results were not recognised as breaches and therefore compliance breach reports were not submitted to the Inspectorate for the October compliance submission.
These errors were subsequently identified by the Inspectorate and the company submitted a failure report.
Bentazone
Two failures within the Thames water Clatford zone where high levels of Bentazone were found in the raw water and the treatment works had insufficient treatment systems in place to be able to remove it, the investigation did not identify a source and the issue could be historic as no farmers were found to be using Bentazone. Concentrations appear to correlate well with ground water levels being high in Winter / Spring indicating that there could be soil contamination which is affected by rain and high levels of ground water.
The Inspectorate had previously issued a notice which is in place and is due to be completed in 2028.
Water quality events
Water companies are required to notify the Inspectorate of any event which, by its nature has, or is likely to, adversely affect the quality or sufficiency of the water supplied to consumers. A notifiable event can also be any incident or occurrence that has caused, or is likely to cause, concern to persons to whom water is supplied. This is an intentionally broad definition to ensure that any occurrence in the water supply is quickly notified to the Inspectorate and that effective remedial action is taken.
In 2024, the Inspectorate was notified of 556 events in England. This is a 4% increase in the number of events reported in 2023 (533 events). The DWI adopts a fair and transparent approach to enforcement and will take action in accordance with the DWI’s enforcement policy in response to event assessments after careful assessment of the facts and circumstances of each incident by the assessing Inspector.
Figure 8 and table 14 – number of reported events per year
Event year
Number of events
2001
430
2002
367
2003
331
2004
308
2005
311
2006
363
2007
361
2008
499
2009
379
2010
349
2011
363
2012
397
2013
405
2014
482
2015
515
2016
486
2017
484
2018
500
2019
499
2020
395
2021
425
2022
465
2023
533
2024
556
The diagram below illustrates the type of the events reported to the Inspectorate in 2024 and their impact on the water supply from source to tap. Some reportable events may have been outside of the company’s control. For instance, over 31% of reported events occurred on consumer premises and were attributed to pipework fittings, cross-connections, materials causing taste and odours, lead pipes, leaching of nickel contained within taps and connectors, improper use or absence of backflow protection and plumbing.
A further 12% of events were due to ground contamination, such as spillages of petrol or other chemicals transcending pipes, and nearly 12% were due to damage by third parties, such as roadworks damage by another company, media interest, vandalism, and other miscellaneous situations where the company has little or no control over. Therefore, approximately 55% of all water quality events reported to the Inspectorate were outside of the control of the water company. The remaining 45%, would have been within the company’s control.
Figure 9 and table 15 – 2024 events in England
Description
Number of events
Vandalism
2
Use of unapproved materials/products
3
Treatment failure upstream of final disinfection
7
Structural failure
12
Satisfactory investigation, did not identify root cause
9
Raw water deterioration
13
Plant failure
23
Planned work
29
Other
87
Microbiological Contamination
28
Mains problem/ damage
65
Ground Contamination / Spillage
69
Gastric Illness – Report from Health Authority
1
Emergency Work
3
Discoloured water – cause unknown at present
8
Cryptosporidium in Final Water
1
Cross Connection
4
Consumers distribution system
174
Company communication pipe problem
14
Back Siphonage
9
Animacules
1
The Inspectorate has developed a series of risk indices to identify where companies should address water quality risks to supplies. For events, the DWI use the Event Risk Index (ERI), which measures the impact of any events and the potential consequence on consumers as well as understanding the actions taken by the company in response. The ERI is designed primarily for the purposes of effective regulation, ensuring appropriate scrutiny is directed to those areas of greatest relative risk. The ERI is not a statutory measure, it does not remove the duty for a company to notify, investigate and respond to every event as set out in the regulations. However, as a risk-based metric, the objective is to incentivise the company to allocate its resources towards highest risk in a precautionary manner.
Figure 10 and table 16 – ERI since 2020, this is a sum of the raw score divided by the total population of each company
Year
ERI
2020
215.0
2021
10354.7
2022
965.8
2023
2072.6
2024
1012.2
Event risk index by company
The ERI identifies companies who require additional regulatory mitigation measures to minimise any further impacts on consumers. The bar chart below shows the relative risk ranking of companies. Four companies; South Staffordshire Water, United Utilities, SES water and The Isles of Scilly are above the industry ERI. For the 2025 reporting year the Isles of Scilly will be incorporated into their parent company South West Waters reporting.
Figure 11 and table 17 – ERI by company for 2024
Company
ERI Score
Median
AFW
0.1
65.0
ANH
316.4
65.0
BRL
10.4
65.0
CAM
34.9
65.0
ICW
0.0
65.0
ISC
19809.6
65.0
IWN
15.6
65.0
LNW
7.3
65.0
NES
323.1
65.0
PRT
2.6
65.0
SES
1469.1
65.0
SEW
28.1
65.0
SRN
974.1
65.0
SST
3975.0
65.0
SVT
60.7
65.0
SWB
154.5
65.0
TMS
106.6
65.0
UUT
6325.5
65.0
WSX
69.3
65.0
YKS
23.3
65.0
ENGLAND
1036.8
65.0
Highest Event Risk Index (ERI) scoring events
In determining the highest risks, ERI identifies those sites which present the greatest need for intervention by way of risk mitigation. The focus is on asset health because of the link to ongoing poor performance manifesting as repeated and ongoing failures to a larger proportion of consumers. Consequently, most of the 556 events notified to the Inspectorate in 2024 were of relatively short duration, and companies took appropriate action to inform and safeguard consumers and liaised with other stakeholders, the risk scores were low.
Figure 12 and table 18 – Top 10 ERI scoring events
Point source pollution of the River Dee with 2-isopropyl-3-methoxypyrazine (IPMP) from a dairy farm
4
5840.28
2024
NES
Use of unapproved Molecor
Use of unapproved materials/products
4
13824
2024
ISC
Elevated Chlorate Results – Tresco
Chlorate > 700 µg/l for multiple samples
4
14485.355
Specific events
Elevated chlorate – Tresco and Buzza service reservoir (St Marys), Isles of Scilly April 2024
Chlorate and chlorite are disinfection by-products that can arise from the manufacturing process, or as degradation products, from the use of sodium hypochlorite, calcium hypochlorite or chlorine dioxide for disinfection or oxidation processes within drinking water treatment and supply systems. Concentrations should be maintained as low as reasonably practical without compromising disinfection. In 2017, the World Health Organization (WHO) Guidelines for drinking-water quality retained the provisional guideline value of 0.7 mg/l for chlorate and 0.7 mg/l for chlorite
As sodium hypochlorite solutions age or temperature increases, the amount of chlorate increases and the amount of available chlorine for chlorination / disinfection decreases. This makes it necessary to increase the volume of sodium hypochlorite solution dosed to achieve the correct level of chlorine which in turn increases the amount of chlorate in supply. At a time where climate change is likely to increase environmental temperatures, this risk is of increasing importance and has been highlighted in previous audits and reports to the industry.
In 2023, the Inspectorate undertook a chlorate audit of South West and Bournemouth Water, which included the Isles of Scilly. As part of the audit findings the company were requested to report (including retrospectively) any breaches of the 700 µg/L chlorate threshold as an event. The company reported two events for the Isles of Scilly in 2024 – Tresco and Buzza service reservoirs.
On the island of Tresco the water supply system comprises of a works and several service reservoirs. South West and Bournemouth Water have undertaken chlorate sampling at the works and the service reservoirs on Tresco since April 2021. Between 2021 and March 2024 a significant proportion of chlorate results from the works and service reservoirs on the island were noted to be > 700 µg/L. The chlorine control system at the works is a legacy system and dosing is via a recirculation system between the two tanks at the works. Sodium hypochlorite dosing pumps were at the time the event reportedly linked directly to a 25-litre drum. The dose was controlled via a chlorine monitor located on one of the tanks.
Buzza reservoir is located on the island on St Marys. Again, the company has undertaken chlorate sampling on the island since April 2021. Two samples taken from the reservoir exceeded 700 µg/L for chlorate in 2022 and 2024. The chlorine dosing system at the suppling works comprised a single 200 litre day tank, and a set of duty / standby dosing pumps. The day tank at the time of the event was filled by decanting 25 litre drums of sodium hypochlorite into the tank.
Following a previous audit in 2021 the Inspectorate made a recommendation to the company regarding the risk of the formation of degradation products (including chlorate) due to the chlorine storage, batching and dosing arrangement on the islands. The company in response amended their procurement arrangements of sodium hypochlorite and reduced the volume of sodium hypochlorite being ordered from 1000 litre bulk tanks and 200 litre bulk product to 25 litre drums.
In 2023, the company improved their stock rotation and sourced a supplier of lower strength sodium hypochlorite and commenced using the lower strength sodium hypochlorite in 2024 after modifying the dosing control at both works. The company furthermore reduced the number of sodium hypochlorite drums ordered, increasing the order frequency and reducing the storage time of sodium hypochlorite on the islands. In addition, the company applied a new internal trigger value for chlorate of 250 µg/L to initiate an investigation. In addition, following the audit the company produced site specific chlorate policies for the islands.
While the company were responding to the increasing challenge of chlorate formation it is necessary to improve further the management of the company’s sodium hypochlorite stock levels on the islands and the response to elevated chlorate results especially those which led to prolonged elevated chlorate levels.
The Inspectorate has served notices for Tresco Water Quality Improvements and St Marys Water Quality Improvements to ensure the company mitigates the known risks.
Precautionary boil advice – Coliform detections – Bryher, Isles of Scilly October 2024
In October 2024, compliance samples taken from the works and service reservoir on the island of Bryher by South West and Bournemouth Water contained a single coliform. The detection of a coliform in a service reservoir whilst not necessarily harmful, may indicate a defect in the asset and a potential risk. This report has highlighted the need to act on any such failure to identify the root cause. Rightly, the company undertook a sampling survey as part of the investigation and detected coliforms at another service reservoir and at consumer properties. In response the company issued a boil water notice was issued for the island to protect public health. Again, this is an appropriate approach.
In response to the coliform detections, the compartment of the reservoir was drained. . The company found a small dead bird near the outlet of the compartment. The inspection identified a small dead bird near the outlet as a result of the gauze protection missing from an air vent.
The company continued sampling, after issuing the boil water notice and E. coli was detected at one of the service reservoirs and at consumer properties reinforcing the validity of the precautionary step to advise water to be boiled.
The reservoirs had previously been inspected in 2021 by a third party and no inspection records had been completed. This serves as a reminder that inspections must have all records in order, especially those which are carried out by third parties to ensure work is completed to the expected standard.
A Notice was served for Bryher water quality improvements which includes coliforms and E. coli.
Southern Water – Testwood plant failure & loss of supply December 2024
When work is being carried out at a water treatment works which is in operation to maintain supply, this makes any intervention particularly difficult and not without risk. The complexity and extent of work ongoing at Testwood WTW by Southern Water certainly fits into this category. Nevertheless, it is appropriate that the company undertakes much needed work to improve the site.
In December 2024, Testwood works was shut down for planned work to integrate pumping station software into the site SCADA. When a works is taken out of supply this can present an opportunity for specialist maintenance which would otherwise be difficult or impossible to complete. In this instance, a specialist valve contractor was employed to ‘rattle’ one of the high lift pump outlet valves. However, a risk assessment for the work did not consider any water quality considerations. This report has highlighted previously the need to carry out water quality risk assessment on any operation to avoid being the cause of an incident.
When the works was restarted high turbidity was recorded and the site automatically shut down. This is a failsafe control to protect public health. Attempts to flush the turbidity were unsuccessful, and the site was run to waste. Further restarts were delayed due to faults with the sodium bisulphite dosing which continued to dose while the works was shut down. This additionally required multiple attempts to flush the high turbid water and the construction of a temporary run to waste facility. As a consequence, downstream reservoir levels ran low and 130,920 consumers in the Rownhams area experienced loss of supply or discolouration between 18 and 31 December 2024.
This is not the first time that a loss of supply event occurred at Southern Water which was caused by work being undertaken by contractors on company sites. A previous event was also caused by poor management of contractors. As part of the investigation into this event, the company stated it would “review arrangements for management of contractors at site to make sure the correct level of supervision is in place” to prevent a recurrence. Recommendations were made for the company to revisit its arrangement for the management of contractors and subcontractors on site. Further enforcement may be issued if there is a recurrence of events of this nature involving contractor management.
The company rezoned the area to minimise the impact of loss of supply, and bottled water stations, bottled water deliveries and tankers were utilised. However, there were multiple issues with the provision of alternative supplies and given similar issues with previous loss of supply events associated with Testwood works, the Inspectorate has now issued a Section 19 undertaking to improve resilience at the works and improve provision of alternative supplies. The works already has a Final Enforcement Order in place for improvements to the treatment plant.
Other notable events
Southern Water – Brede WSW High Chlorate August 2024
Ongoing maintenance is essential when dealing with drinking water infrastructure. However, with any live site scheduling work can be difficult if the very equipment requiring maintenance must stay operational. In which case appropriate plans must be put in place and it should not be deferred.
On such situation arose when pipework on the main hypochlorite dosing pumps at Brede works began to leak filling the bund underneath the main hypochlorite storage tank. The leaking dosing lines had been a known since at least January 2024 and not acted upon for months. Instead, the hypochlorite in the bund was being tankered away from the site approximately once a month by a third-party contractor. A change in procedures by the third-party contractor outside of the companies control and with no mitigation in place led to a delay in the removal of the bund contents. To prevent the bund overtopping the company decided to return the contents of the bund to the dirty wash water tank where it could be blended with backwash water and returned to the works inlet on three separate occasions for a total of three hours and 45 minutes.
A risk assessment by the company underestimated of the pumping rate, the chlorine concentration and the bund size. In addition, the risk assessment, while it considered trihalomethane (THM) formation as a risk, did not consider chlorate as a risk and was focussed on avoiding an environmental pollution incident. This was not putting drinking water quality first.
Approximately two buckets of dechlorination tablets were added to the hypochlorite to reduce the risk of THM formation, however the dose was not calculated, nor were subsequent chlorine levels measured. These tablets were not approved for use under Regulation 31. This was not putting drinking water quality first.
Between 29 July and 1 August 2024, routine samples were taken from the final treated water sample point at Brede works, from Fairlight Ore service reservoirs (SR) one and two and Warren Fairlight and Udimore reservoirs. Results were obtained between 4 and 6 August 2024 reporting chlorate concentrations of 735 µg/L and 921 µg/L from Fairlight Ore 1 and 2 reservoirs, 695 µg/L from Warren Fairlight reservoir, 415 µg/L from Udimore and a chlorate result of 1,340 µg/L from Brede final treated water. This outcome did not consider water quality.
The company completed a public health risk assessment to understand whether illness was likely to occur at the concentrations supplied. This assessment concluded that the risk of illness was low. UKHSA completed an assessment of public health risk which also concluded that the risk to public health at the concentrations seen and time of exposure was low. A formal investigation was mounted by the Inspectorate which included an audit of the works, witness statements from company staff and issued consumer questionnaires.
National conditions of use for electrolytically generated sodium hypochlorite state that the treated water must not contain chlorate greater than 700 µg/L. Additionally, unapproved dechlorination tablets were used prior to returning hypochlorite to the works inlet.
As such, the Inspectorate considered that there was evidence that offences under regulation 33(3) may have occurred and a warning letter was issued to the company. Water companies should take note that failure to maintain drinking water assets has serious outcomes and must be prioritised to protect public health.
Southern Water – Wingham – Nitrates above PCV April 2024
Nitrate occurs naturally in all surface water and ground water although higher concentrations tend to occur only where fertilisers are used on the land. It is produced during the natural decay of plant matter in soil. Rainfall washes nitrate out of the soil and into surface water such as lakes, rivers and streams. Nitrates can also seep down through the soil and be found in groundwater. Whilst it is generally low in waters in England, very high amounts of nitrate in drinking water can cause adverse health outcome in very young children. It is therefore a tightly regulated parameter upon which the standard is based on the World Health Organisation’s guideline value for drinking water, which is 50 mg/L.
On 20 April 2024, Southern Water was informed by its laboratory service that two nitrate samples had exceeded the prescribed concentration for nitrate of 50 mgNO3/L. One of these had been collected on 19 April 2024 from the treated water tap at Wingham works, with a nitrate concentration of 50.5 mgNO3/L. The other had been collected from a reservoir downstream of the works and reported a nitrate concentration of 51 mgNO3/L. This service reservoir is normally supplied from Wingham works. In response to these sample results, the company rezoned the service reservoir onto a supply from a different works.
The event was caused by the reliance on a single nitrate monitor at the works, whose readings had drifted downwards and was therefore providing inaccurate readings, resulting in the company failing to prevent Wingham works from supplying wholesome water with a nitrate concentration within the regulatory limit. This is not putting drinking water quality first because critical control points must have appropriate calibration on health-based parameters and preferably a secondary system to identify risk early. While it may be considered that laboratory analysis represents a secondary system, the company had experienced two other events linked to elevated nitrate concentrations in the previous 12 months. As the site was a known risk a secondary monitor would have been a minimum mitigation.
Following the Wingham event, the Inspectorate recommended that the company reviews the maintenance / calibration of nitrate monitors and installs additional validation monitors at all of its sites which are potentially at risk of breaching the regulatory limit for nitrate. The Inspectorate has previously issued a notice for the site requiring the company to install and commission ion exchange treatment for nitrate removal by 31 December 2025 securing the supply for the future.
Southern Water – Hastings loss of supply May 2024
In the early morning of 2 May 2024, Southern Water’s Beauport works shut down and could not be restarted as no raw water was being received from the Darwell raw water reservoir.
The company received 731 consumer contacts between 2 May and 8 May 2024 with 718 of these reporting loss of supply. The event was caused by a burst on the 800 mm concrete raw water main between the Darwell raw water reservoir and Beauport works.
The company previously applied for and was granted planning permission to replace the main in 2006. The company state in the non-technical summary document accompanying the planning application that the pipeline is of strategic importance to the continued security of drinking water supply to the Hastings area. The non-technical summary also states that over the past few years (prior to 2006) the pipeline suffered from a number of bursts and is now approaching the end of its useful life and that taking no action is not an option.
Due to the recurring theme of loss of supply/supply resilience associated with past events, a similar event will most likely recur until the company implements improvements to its supply system and that enforcement is now necessary to secure actions to prevent a reoccurrence. To ensure the company acts upon this high priority main, the Inspectorate has now issued a Section 19 undertaking for the main under SEMD.
Companies are reminded that critical assets such as raw water mains must be maintained and replaced where the asset is repeatedly failing causing a loss of supply.
Anglian Water – Welton works – Clostridium perfringens detections December 2024
Welton Works is a groundwater site supplying part of the Grimsby Skegness and the company detected clostridia on 6 June and 23 June 2024 and three coliform and one E. coli detection from 2023. Clostridium perfringens is used as an indicator species for historic and/or intermittent faecal contamination in drinking water. The size of Clostridia spores means that they can be a useful surrogate for Cryptosporidium and their presence on a system with a physical barrier process such as filtration may indicate that it has been less than effective and, consequently, the supply may be at risk from Cryptosporidium (Technical guidance on Microbiological Contaminants, Drinking Water Quality Regulator for Scotland).
The company considered that “The root cause of the UV outlet Clostridia is not thought to be due to filter performance.” However, a review by the Inspectorate noted that the individual filter flow trends on both 10 November and 20 December, at the exact time the samples containing the Clostridium perfringens were taken, RGF 3 was undergoing a filter backwash. The residence times in the filters, contact tank, new reservoir and old reservoir North/South equates to approximately 23 hours. For both Clostridia detections in November and December, RGF2 was undergoing a backwash approximately 23 hours prior to the time of the sample being taken.
These anomalies and the increase in turbidity being observed following a filter wash are signs of breakthrough at this stage of the treatment process. The company has been aware of these filter performance issues for some time and following a minded to consider enforcement within the audit assessment letter, the company provided reassurances to the Inspectorate that focussed investigations and appropriate remedial actions would be taken in a timely fashion
The Inspectorate was critical that the RGFs are likely to be outside of the scope of filtration performance required at this site since without individual turbidity monitors and head loss monitors on each filter, the filter performance cannot be verified. Five separate confirmed Clostridia detections lead to the potential that adequate filtration is not being achieved at Welton works. Similarly critical was the conclusion are the log reduction credits which are being assigned to the filters because the company cannot adequately show compliance with the requirements for the preliminary treatment of water prior to disinfection
The company has installed UV treatment at Welton works as an additional safeguard but not assigned it as part of the disinfection process at the treatment works, and Ct is met with chlorination only which is not commensurate with the function of the process or the intent of the regulation.
The Inspectorate provided the company with numerous occasions and ample opportunity to address the ongoing issues at Welton works. Consequently a Regulation 28(4) Notice for Welton works to secure compliance with bacteriological standards for drinking water quality was issued on 13 February 2025.
Yorkshire water – Longwood – Loss of ferric sulphate dosing July 2024
Ferric sulphate is a versatile and effective chemical used in water treatment the coagulation and flocculation of particles reducing turbidity in water ready for the next step of treatment which is filtration. Without coagulation, turbidity rises making it less efficient for filters to remove contaminants.
An investigation into recent data trends from the works revealed a loss of ferric sulphate dosing which had occurred on 3 July 2024. The automated coagulant control system was in a fault state as there was no flow. To rectify the issue the control system was stripped and cleaned. However, on completion of the work, it was noticed that the flocculation stirrers had ceased operation and the ferric dosing pumps were not running. Attempts to restart the pumps caused the shutdown alarm to initiate and reset within 600 seconds. As a result, the automatic shutdown did not occur and the works was shutdown manually.
The works was restarted at 15:00 on 3 July 2024. Later that evening, the turbidity from the rapid gravity filters started to increase. The inlet flow to the works was reduced and it was concluded that the rise in RGF turbidity was likely as a result of the works shutdown earlier that day. The turbidity was monitored and once it had reduced, inlet flow was increased again. Subsequent discussions with the site team confirmed that they had made a decision not to run the site to waste following the restart of the works because the turbidity levels were not considered sufficiently high to require it.
On 4 July 2024, Yorkshire Water reported a compliance sample from the works which contained coliform bacteria at a concentration of 4 per 100 ml. The impact of the connected circumstance of the coagulation failure and the the decision not to run the non-coagulated water to waste provides a learning to companies of the criticalities of such decisions in the absence of a water quality lens.
The Inspectorate gave a recommendation for the training related to the escalation of critical treatment processes to be reviewed to ensure escalation procedures are followed and documented. This serves as a reminder to water companies of the importance of robust escalation practices in safeguarding water quality.
United Utilities – Lightshaw – consumer contacts July 2023
The importance of communication by companies about drinking water when there are changes are critical to maintaining confidence in drinking water. This is because consumers notice even slight changes in their drinking water and become concerned if there is a change which is unkown to the consumer, even if the drinking water as supplied is perfectly safe to use.
This event occurred following a planned change of source water by United Utilities at a site supplying consumers in the areas of St Helens and Wigan in July 2023.
Lightshaw works was returned to supply on 21 July 2023. One of the areas affected was a relatively new district metered area (DMA) that that was established between 2022 and 2023.
Between 24 July and 6 September 2023, the company received 120 contacts from consumers in water supply zones (WSZ) 120 and 125, expressing water quality concerns. The company also received a total of 366 written complaint letters from consumers located in the new DMA. Due to these complaints the company rezoned the network in September 2023 to supply that DMA from another zone fed from the Manchester ring main.
The change in source is an action that is undertaken by the company from time to time. While both sources provide wholesome water, the difference in source water chemistry results in a noticeable change in appearance, taste or odour for consumers. This can be managed by effective and timely consumer communications to pre-warn them of the change. Although the company carried out a risk assessment before returning Lightshaw works to supply after the change of source, the risk assessment failed to adequately consider the effect of source water change on consumers, especially those who had not previously received a supply from Lightshaw works. The company did send proactive communications to consumers to inform them of a planned change to the water supply, however the reassurance was inadequate and did not reach all consumers affected.
The Inspectorate carried out consumer questionnaires and took statements that provided evidence that consumers had rejected the water for drinking, cooking, and washing even though the water was perfectly safe to use. Consequently, the requirements of the regulations require a conclusion that the company had supplied unwholesome water following the change in source for Lightshaw works because it imparted a noticeable change to the appearance, taste and odour of the water supply which consumers did not find acceptable.
The company were issued with a warning letter on 4 July 2024. The event highlights the importance of comprehensive risk assessments and effective consumer communication when altering source water supplies. This also underscores the need for better anticipation of consumer acceptability issues, targeted communications, and more robust implementation of lessons learned from past incidents when considering future changes.
Thames water – Fuel contamination in Bramley, Guildford
Petrol and diesel create problems for drinking water pipes as hydrocarbons can pass through plastic mains pipes and create an odour in water at extremely low levels. One such situation arose when a long running and high-profile event concerning low level contamination of the mains supply with fuel, that is benzene occurred in Bramley, Guildford.
In August 2023, Thames Water were made aware of a significant historic fuel leak from a tank at a petrol station in the Bramley area. Due to the known risk of migration of hydrocarbon compounds from the soil through some water pipework materials, a review of local consumer contacts was carried out. It did not indicate that the fuel leak had impacted on water quality in the area, but investigatory sampling was carried out and a hydrant chamber was found to have a fuel odour, although a flush of the main confirmed no odour issues with the water supply itself.
No further issues were experienced until a consumer reported a ‘white spirit’ taste and odour in October 2023. Analytical results identified fuel-related hydrocarbon compounds above aesthetic operational levels, but below short-term health limits at the property and at a neighbouring property. Advice not to drink the water was provided to the two properties and bottled water was delivered by the company. In January 2024 the communication pipework to the two properties was replaced with specialist barrier pipework which is impervious to fuel transmission through the pipe wall. The restriction of use advice was rescinded following satisfactory confirmatory samples at one property on 9 February and the other on 5 March 2024.
Thames Water proactively sampled the wider area in October 2023 through which low levels of hydrocarbons were detected. Thames Water determined that no short or long-term health impacts were anticipated at these levels, but the company took the decision to continue water quality analysis and monitoring around Bramley. The company also continued engagement with the Local Authority, UKHSA (UK Health Security Agency) and third-party environmental consultants in relation to the fuel leak and the steps to remediate the contaminated land.
A water quality sample collected in April 2024 identified concentrations of benzene above the prescribed concentration (PCV) in a public building in close proximity to the historic fuel contamination. Analytical results of further samples taken in late April and early May 2024 were below the prescribed concentration.
A hydrocarbon odour was detected by one of the three analysts on the odour testing panel from a sample collected from the public building on 14 May 2024 (considered a pass under the standard methodology). However on risk assessing the findings, the company issued restriction of use advice for the property. Subsequent analysis of the same samples taken on 14 May 2024 identified benzene above the PCV and alternative water supplies were provided to the public building.
Samples collected on 28 May 2024 from another location in Bramley contained benzene above the prescribed concentration (PCV). The risk assessment was updated to reflect this deteriorating trend in hydrocarbon concentrations in the area, and the company decided to issue do not drink advice to a wider area of Bramley containing 622 properties on 30 May 2024. Letters informing consumers were hand delivered to affected properties. Bottled water stations were opened the same day with bottled water delivered to vulnerable consumers. Arlington tanks were deployed to provide an alternative water supply to local schools.
The company continued to monitor water quality, and reviewed remediation options. Pressure management plans were implemented to contain the issue to as few properties as possible. Routine flushing was also implemented to reduce the hydraulic residence time and therefore the concentration of benzene in the water mains.
Sections of MDPE water main that were in close proximity to the contaminated ground and therefore subject to hydrocarbon permeation were replaced with barrier pipe. This was a complex operation as additional safety controls were needed to address combustion risks, this was completed and commissioned on 26 June 2024.
The issue of the wider restriction of use notice to properties in Bramley attracted significant media interest. The company issued media statements throughout May, June, and July 2024. To keep consumers informed, a frequently asked questions web page was produced, and laboratory data was also shared with weekly updates.
Following remediation efforts, verification through water quality samples and consultation with public health stakeholders, the restriction of use notice in Bramley was rescinded on 3 July 2024.
Thames Water’s proactive monitoring programme since October 2023 ultimately led to the identification of the mains contamination from a third-party source and contributed to establishing an appropriate course of action (installing barrier pipe) to address the issue. The company continues to risk assess and monitor the situation in Bramley. The analytical results from 3 July to 19 September 2024 showed some very low levels of hydrocarbons in some samples. However, analysis since 24 September 2024 shows no further detection of fuel-based hydrocarbons in the water supply .
Asset health and service reservoir integrity
During 2024, there were 80 compliance failures for coliforms at water treatment works and 122 at reservoirs. There were three E. coli detections at treatment works and seven at reservoirs from a total of 3,631,092 tests. Ingress into contact tanks and service reservoirs is a recurrent problem and represents a residual risk as these results show.
In addition to these compliance breaches, there were 38 water quality events attributable directly to poor asset health and plant failure, including seven failures of the disinfection system and 12 structural failures of the treatment works, tanks or reservoirs. The expectation is that companies understand and maintain their assets through a programme of physical inspections, which may be supplemented with inspections by remotely operated vehicles (ROV). The Inspectorate considers physical inspections as being necessary because they provide clarity and better resolution than ROVs and allow for cleaning of walls and structures within the reservoir. Whilst 10 years is the maximum interval advised in the Principles of Water Supply Hygiene on treated water storage, the Inspectorate recommends more regular inspections are carried out on on a risk-based frequency.
Over the past five years the Inspectorate has increased scrutiny of service reservoirs and tanks through the service reservoir and tanks data return to ensure the quality of inspections and the robustness of remedial works. Analysis of the new data set highlighted gross failings around frequencies of inspections with 233 tanks not having been inspected for over 10 years. This represents an average of 3.1% compared to 2023’s 4.9% and 2022’s 6%, this is a significant improvement in the industry picture but reservoirs still represents a continuing risk requiring attention.
Figure 13 and table 19 – number of service reservoirs per company and the percentage overdue for inspection
Company
Assets
At risk
Percentage at risk
PRT
35
6
17.14%
SEW
322
38
11.8%
SRN
336
21
6.25%
HDC
118
7
5.9%
SWB
500
25
5%
ANH
776
35
4.51%
SES
75
3
4%
TMS
659
22
3.34%
SVT
868
25
2.88%
NES
526
13
2.47%
AFW
246
6
2.44%
UUT
641
13
2.03%
WSX
566
9
1.59%
BRL
187
0
0%
SST
68
0
0%
YKS
724
0
0%
VWP
6
0
0%
CAM
39
0
0%
DWR
696
0
0%
Despite its low numbers of assets Portsmouth water has 17% of reservoirs which have not been inspected within the required frequency
Events relevant to asset health in 2024
Southern Water – Dunkirk Break Pressure tank ingress
In October Southern Water undertook a remote operated vehicle (ROV) survey at Dunkirk break pressure tank. The survey was a reinspection following a previous one in March 2024, to identify any new anomalies or potential points of ingress. Dunkirk break pressure tank is an asset which cannot be removed from supply for physical inspection and as such is covered by a regulation 28(4) notice which includes steps for the company to make the necessary enabling works and undertake ROV surveys as an interim measure.
The ROV identified suspected ingress in two places on the roof/wall joint. A sample taken on the same day from the tank reported a single coliform. The company applied overbanding externally to the areas of suspected ingress and have arranged for enhanced sampling and 3 monthly ROV inspections until the reservoir is able to be removed from service. A bypass needs to be installed to enable removal from service however, this has been delayed due to installation and commissioning of enabling works. The company expects to be able to complete this in May 2026, and will be installing a new roof membrane as a short term mitigation measure.
Thames Water – Animal Ingress in Farnborough Service Reservoir
A routine inspection completed by the company of Farnborough service reservoir on 14 March subsequently identified five rodent carcasses, the tank was isolated in advance of the inspection on 6 March. The company’s investigation concluded the most likely route of entry to be breaks in the ventilation system below the roof membrane level. The service reservoir supplies a maximum population of 209,468. A review of downstream consumer contacts the month prior to identification of the ingress confirmed no illness complaints. Sample results from routine monitoring programme in addition to samples from downstream locations did not detect the presence of E. coli or coliforms in the period preceding the removal of the tank from supply.
Southern Water – Baldslow service reservoir ingress
Following a consumer complaint of illness in April 2024 Southern Water undertook investigative sampling, including collecting samples from the supplying service reservoir. Although the sample at the consumers property did not contain any bacteria, however coliforms were reported in a sample taken from the upstream Baldslow service reservoir. The reservoir was removed from supply and ingress was identified. The points of ingress were repaired and a new roof membrane was installed in July before being returned to service.
Southern Water – Service reservoir
In May, a Southern water service reservoir in Sussex was removed from service for a routine flood test and inspection. The service reservoir had previously been inspected in January 2016 with no issues identified at the time. Two leaks were identified around the access covers, and a further inspection identified root ingress from trees in a neighbouring property. The company removed the cell from supply to enable the repairs to be completed and the cell was returned to supply in July following the completion of the works.
Southern Water – Wigmore 2 service reservoir ingress
In April, the company undertook a ROV survey and drop test of Wigmore 2 service reservoir ahead of a planned drain and clean. The ROV identified possible hairline cracking on the roof, and the drop test showed evidence of leakage. Due to a lack of flowmeters, the company could not confirm if the drop in level was due to a valve letting by or due to structural issues. The service reservoir was removed from supply and a flood test conducted, which confirmed multiple points of ingress. The Inspectorate reminded the company of the role of flowmeters in identifying uncontrolled or unmitigated flows and suggested the company identifies treated water storage assets where flow meters are not present and develops plans to install them.
Southern Water – Brede works Harland Tank potential ingress
in July 2023 an ROV survey was undertaken on the Harland tank which is pump suction tank at Brede works. The inspection identified potential points of ingress however the findings from the survey were not reported or escalated at the time. The findings from this survey were escalated in January 2024 after a coliform detection in an operational sample taken from Brede works. The Brede Harland tank requires enabling work to remove the tank from supply as it contains the backwash water pumps. The company has put in place short term measures including enhanced monitoring and the Inspectorate issued a regulation 28(4) notice following this event so that the company has defined short term measures and can plan and undertake the required remedial works to be able to remove the asset from supply. The Inspectorate also recommended to the company that the include defined escalation steps and procedures following any issues identified during ROV surveys.
Thames Water – Potential Ingress at Hampton works
A remotely operated vehicle (ROV) inspection of the contact tank outlet chamber was conducted. The inspection identified ingress of rainwater on roof joints. In response to the identified ingress Thames Water repaired the external membrane around upstands of kiosk buildings above the chamber. Sump pumps were also installed to displace accumulating rainwater. A scaffolding structure was constructed over the outlet chamber building to further protect against rainwater. Improved drainage channels were also installed.
South Staffs Water – Overpark service reservoir east
E. coli was detected in the east compartment of this two celled reservoir in July. The east compartment was subsequently removed from supply. Whilst the internal inspection identified no ingress, the company’s investigation identified an increased risk of aged water returning to reservoir from the network based upon demand. Under normal circumstances, booster chlorination is used to maintain sufficient residual disinfectant to this part of the water supply network, however, the dosing facilities tripped several times in the days before the E. coli detection, but alarms were not sent to the control room due to communication issues. These circumstances occurred before in June 2023 following a microbiological failure at Overpark service reservoir west compartment. Further work is required by the company to improve the turnover of water in this reservoir to prevent a repeated occurrence.
Northumbrian Water – Elford Reservoir
An operational large volume sample taken on 31 May 2024 from the SR contained 3 E. coli/1000 mL. Elford SR is included in NES-2020-00011 Tanks and Service Reservoir notice and the large volume sample was taken as required by this notice. The SR was removed from supply on 1 June 2024, four hours after the presumptive E. coli was reported to the company.
A dip sample was taken from the SR on 1 June 2024 and a sample from the sample tap prior to the SR being removed from supply. These samples contained E. coli and Enterococci. This sampling was repeated on 2 June 2024. All samples were analysed for standard microbiological parameters and Clostridium Perfringens and Enterococci and were satisfactory for all parameters, except from the isolated SR which again confirmed the presence of Enterococci.
An external audit was carried out on 3 June 2024. Air valves upstream of the SR were checked as part of the investigation and were found to be satisfactory. There was no evidence of poor drainage, however parts of the embankment had slipped, and the reservoir structure was visible.
An internal inspection and flood test of the isolated SR was carried out on 5 June 2024. Ingress was found on a joint between the roof and wall structure, in a location with external embankment slippage.
Issues with the overbanding were also found. Following the inspection, the embankment was backfilled and the overbanding was either repaired or replaced. The external waterproof membrane on both upstands for the access hatches was replaced following ingress detection during a second flood test and both access hatches have been lifted and resealed.
Anglian Water – Boughton Reservoir
An internal monitoring sample collected from Boughton Reservoir on 24 October 2024, was reported to contain four confirmed coliforms in a 100 mL sample. Further coliform detections were reported from Boughton Reservoir in both large volume 10 L samples and in routine 100 mL sample.
A remotely operated vehicle (ROV) inspection of Boughton Reservoir was completed in July 2024 (before the coliform detections) and repeated on 28 October 2024, with no changes or issues noted between the two inspections. Boughton Reservoir was removed from supply on 17 December 2024 and was internally inspected on 21 January 2025. The full internal inspection found six points of ingress at roof to wall joints, the western roof expansion joint and 17 wall joints; along with other integrity issues requiring remedial works.
ROV inspections alone may not be sufficient to identify all integrity issues—Boughton Reservoir, despite recent ROV assessments, had undetected ingress points that contributed to water quality failures. This underpins the importance of periodic full physical internal inspections.
Consumer contacts
The acceptability of drinking water is ranked by consumers as their top priority, and can be affected by several factors including its appearance for example, discolouration or aerated, or the taste and/or odour. Most acceptability complaints are caused by a black, brown, or orange discoloration of water which are caused by elevated concentrations of manganese, iron, and aluminium.
Whilst these metals are rarely at a concentration which is harmful to health, they can and do cause widespread rejection of water based upon appearance. The expectation and priority of a consumer is for their water to be clean and safe, and therefore, events which cause discolouration are highly disruptive to consumers with the inevitable drop in confidence which follows. The Inspectorate takes these events very seriously and many companies have notices in place to focus on the root causes of discolouration.
In February 2024 the Inspectorate issued information letter 01-2024 ‘Annual Provision of Information on Consumer Contacts’ which set out new requirements for companies to report a greater level of detail on their consumer contacts which included the following additional requirements:
A unique reference for each contact
Details of the district metered area the contact is located in
The date and time of the contact
The location of the contact
The mode of contact
Whether the contact is a repeat within a 12-month rolling period (that is a new occurrence or ‘case’ of a similar issue from the same consumer)
If the contact is associated with a notifiable event, and the associated event reference number
Information regarding multiple contacts, for example if a consumer reports more than one drinking water quality concern during a contact, is also recorded.
The data submitted from companies in 2025, covering 2024 is the first submission to include this additional data. To maintain continuation of a comparable data set and monitor industry performance and progress, the new data return allows companies to continue reporting multiple descriptors as either primary or secondary contacts as they have before, with only primary contacts used to monitor ongoing performance.
In England in 2024 there were 70,507 consumer contacts regarding acceptability of drinking water, reported to companies wholly or mainly in England. This is a rate of 1.21 per 1,000 population. The table below shows the number of contacts received for each type of complaint for English companies, with contacts relating to discoloured water (brown, orange, black) being the most common reason.
Category
Contacts
Appearance – Brown black orange
28,974
DWQ Concern – Lead and analysis
7,486
Appearance – White Air
8,386
Taste Odour Other
8,606
Taste Odour Chlorine
6,768
Appearance – Particles
6,427
Illness – Gastroenteritis
5,330
Appearance – General Conditions
5,516
Taste Odour Earthy Musty
3,736
Illness – Skin
1,527
Appearance – Blue Green
1,074
DWQ Concern – Lifestyle
769
Appearance – White Chalk
491
Taste Odour Petrol Diesel
447
Illness – Oral
443
Illness – Medical Opinion
303
Appearance – Animalcules
252
DWQ Concern – Campaign
197
DWQ Concern – Pets Animals
242
Table 20 – Number of consumer contacts in 2024
Discoloured water
Discoloured water usually occurs following flow changes in the drinking water network which re-suspends existing sediment in the mains pipework. Occasionally, due to planned work such as valving, or following bursts or periods of high demand, flow changes can occur. Flow changes, which can result in resuspension of sediment, should be managed by companies. In 2024 around 40 events in England were reported where brown, black or orange discolouration was experienced by more than one consumer at the same time.
The Inspectorate reviews consumer contact data for discoloured water contacts on an annual basis. Companies whose performance is poorer than the industry average are investigated, and enforcement action taken where necessary. Companies with legal instruments in place have a higher risk of discolouration and are:
Companywide discolouration performance is considered when serving notices, in addition to individual water supply zone performance. When completed, these legal instruments will improve water quality to consumers supplied by these companies.
The number of contacts reporting discoloured water (brown, orange or black) across the industry (England and Wales) over recent years has been decreasing, however 2024 has seen a slight deterioration on the previous year’s performance. In England, the rate follows a similar trend and has also seen a slight deterioration in 2024, from 0.4 contacts per 1000 population in 2023 to 0.42 contacts per 1,000 population in 2024.
The England company ranking can be seen below. Of note is the position of South East Water, who have seen a deterioration from 9th worst performing company in 2019, to now being 3rd worst performing.
Whilst other poorly performing companies are improving, the performance of South East Water has not, resulting in them moving up in the ranking over time.
Following the industry trend, most companies under discolouration notices have reported a slight deterioration in contact rate in 2024 compared to that in 2023. However, Southern Water, United Utilities and Wessex Water have improved their contact rate in 2024, with United Utilities and Wessex Water showing a continuing downward trend.
South West and Bournemouth are on a deteriorating trend since 2022, now at a higher contact rate than five years ago. South West and Bournemouth remain the worst performing company in England.
Events related to consumer acceptability
South West & Bournemouth discolouration event
In July 2024, South West and Bournemouth Water reported a discolouration event following a burst on a 20 inch section of the Cornwall spine main located near Summercourt in Cornwall. The spine main is part of a strategic dual main system which feeds large parts of Cornwall. The spine main at this point supplies approximately 84,700 properties in the areas of Padstow, Truro, St. Columb, Perranporth, St. Agnes, Redruth, Carbis Bay. Following the burst the company undertook network changes to minimise the impact of the burst and isolated the section of burst main to complete repairs. The repairs were completed the same day and the company began to recharge the main with flushing completed and turbidity being monitored in the network as part of the company’s risk assessment. The main was fully back in supply in just under 24 hours of the burst occurring, with the network returned to its normal operating configuration shortly after. The impact of the burst caused both loss of supply and discolouration, with around 800 consumers contacting the water company to report discoloured water and around 500 to report no water. The burst occurred during a time when a service reservoir was out of service for planned repairs, which also caused a loss of supply, low pressure and media interest event in the downstream network. Following these events, the company undertook a root cause analysis which identified the need for the service reservoir to be in service during high demand periods such as the summer. The Inspectorate made recommendations to the company surrounding its resilience plans in the areas and consideration of the need for the service reservoir to sustain demand when undertaking planned work and on the triggering and provision of alternative water supplies as stipulated in the Emergency Planning Guidance.
These events demonstrate the scale and impact that a strategic mains burst can have on the downstream network, compounded during a period when an asset is out of service for planned maintenance. The function of strategic mains and how these support downstream assets and supply systems should be fully understood and companies should have appropriate risk assessments, resilience and contingency plans in place to minimise impacts to consumers for water quality and supply, should an event occur.
United Utilities Cumwhinton discolouration
Also in July 2024, a burst main on a cast iron trunk main near United Utilities’ Cumwhinton treatment works resulted in over 300 consumers contacting the company to report discoloured water.
A technical post-incident review identified discrete pockets of consumer contacts, each with individual root causes that led to the resuspension of historic mains sediment within the network. Continuity of supply to customers was maintained through the use of reservoir storage, alternative supply vehicles injecting into the network, and multiple network interventions. Targeted flushing activities were also undertaken in response to discolouration contacts. As part of the learning from this event, suggestions were given to the company around the internal cleaning and inspection of compartment 1 of Cumwhinton (Combined) reservoir, and to review and add the affected DMAs to the company’s flushing programme for 2025/26.
Companies should strengthen their approach to managing discolouration risk by applying the lessons from this event, specifically targeting mains sediment control, network interventions, and proactive reservoir maintenance. With the aim to reduce the future risk of discolouration and improve resilience against similar incidents in the future.
Similar to discoloured water contacts, the rate for total taste and odour contacts for the industry has gradually reduced year on year, although in 2024 this rate has deteriorated to 0.25 per 1,000 population from 0.22 in 2022 . In England, this rate is slightly lower in 2024, at 0.23 per 1,000 population, however this is still an increase from 0.21 in 2022.
United Utilities – Cheshire and Merseyside customer contacts taste and odour event
United Utilities received a total of 968 contacts, of which 786 were for taste and odour, between 5 August and 31 August 2024, from consumers in water supply zones (WSZs) supplied by Huntington and Sutton Hall water treatment works. Huntington and Sutton Hall works abstract from the River Dee and supplies a combined population of 1,904,568 across Merseyside and Cheshire. Following investigations, the company concluded that the likely root cause of the taste and odour to be point source pollution of the River Dee with 2-isopropyl-3-methoxypyrazine (IPMP). The company identified that a dispensing system, which had an automatic wash system was discharging to surface drainage. Although the system was installed in November 2023, it was moved and connected to the surface drainage on 27 May 2024. On finding the source of the IPMP, the company worked to rectify the drainage arrangements on 23 August 2024.
There are no previous examples of contamination caused by this compound within the industry. The DWI concluded that the company breached the limits set out in Schedule 1 of the regulations which requires that there must be no abnormal change in taste and odour.
The company were also quick to implement the scientific investigations in August 2024 that lead to the identification of IPMP and the tracing of the source.
The Inspectorate would expect all water companies to implement learning from this event across all their catchment risk assessments.
Following the conclusion of the event the Inspectorate audited United Utilities’ Huntington and Sutton Hall works in November 2024. The Inspectorate requested a process controller to be present during the two-day audit, however, contrary to expectations, this did not occur. The Inspectorate reminds companies that it is always beneficial to have competent, trained and informed site operators present during a works audit to answer any questions regarding the day-to-day operation of the site.
Seven recommendations were given in total, with several under regulation 27, including to update the site risk assessments with site specific control measures; to develop a procedure and process to regularly verify the powdered activated carbon (PAC) dose at both Huntington and Sutton Hall works; to implement regular cleaning of all clarifiers and clarifier inlet channels at Huntington works due to the significant build-up of floc and sludge; to implement better control measures, to prevent contamination from buffers and reagents; and for regular maintenance and cleaning to be undertaken on the Actiflo streams at Sutton Hall works.
Enforcement was initiated under regulation 28(4) at both sites for shortcomings in the PAC dosing, filtration maintenance and management, and contact tank inspection philosophy at Huntington works and for deficiencies in the PAC dosing system and filtration management at Sutton Hall works.
Severn Trent Water – Chester customer contacts taste and odour
The River Dee also supplies water to Severn Trent Water’s Boughton works, which supplies Chester and the same compound that caused the issues outlined above also occurred here. On 6 August, United Utilities advised Severn Trent Water of a significant increase in musty taste and odour complaints received from consumers supplied by United Utilities’ Huntington works, located upstream.
In response, Severn Trent Water merely reviewed the number of consumer complaints in its own supplies, which was low and initially took no further action. United Utilities subsequently advised that the compound detected was IPMP and Severn Trent Water supported a catchment investigation sampling on 24 August. United Utilities advised Severn Trent Water on 29 August 2024 that the likely source of pollution was a dairy farm upstream of Huntington works.
Severn Trent Water subsequently implemented hourly odour checks at the River Dee intake and the final treated water point at Boughton works, alongside further sampling for a suite of ‘musty causing’ chemical compounds, including IPMP. However, the limitations of the IPMP method meant that it was over 30 times less sensitive than required to detect odour breaches at the threshold level.
Sample results between 20 August 2024 and 10 September 2024 reported:
Indicative concentrations of IPMP up to 1.486 ng/L from samples collected throughout Boughton works and the Chester supply system between 21 August and 28 August 2024.
Concentrations remained significantly below the compound’s 24-hour health-based limit of 135 µg/L (equivalent to 135,000 ng/L) and 7-day health-based limit of 54 µg/L (equivalent to 54,000 ng/L).
Sample results indicated that the concentration of IPMP decreased in the raw water (<0.34 ng/L) from 23 August 2024 onwards and levels were higher in the downstream network, suggesting the potential peak of the pollution had passed through the works to the downstream network.
Earthy or musty taste and odour detections for samples collected from Boughton works final and the Chester supply system between 22 and 29 August 2024.
All the other sample results were satisfactory, apart from a microbiological detection caused by a dirty tap.
The main treatment control for IPMP at Boughton works is granular activated carbon (GAC) filters. Although Severn Trent Water considered the GAC treatment stage was meeting all site performance targets this did not effectively address the treatment issue. The company could identify no other treatment optimisation options to increase the removal of IPMP at Boughton works.
The company removed some musty water by flushing targeted areas to reduce taste and odour impact based on consumer contacts from 22 August 2024 to 30 August 2024 when the flushing ceased after a low level of consumer contacts for three consecutive days.
The Inspectorate audited Boughton works in November 2024 and identified the following relevant issues.
The company’s GAC replacement/ regeneration plan is risk based considering pesticide removal. The effectiveness of taste and odour removal is not considered.
Severn Trent Water’s policy to regenerate the GAC media on a five yearly basis was not always achieved. The regeneration dates are clustered and therefore there is a risk of exhaustion across the whole works at similar times. Two of the six beds exceeded the five year threshold.
The design assumptions for iodine number and empty bed contact time do not appear to be in line with good industry practice.
GAC regeneration
Previous regeneration date
Most recent regeneration date
GAC 1
July 2015
January 2021
GAC 2
August 2018
January 2020
GAC 3
July 2015
March 2020
GAC 4
September 2015
February 2020
GAC 5
December 2015
February 2022
GAC 6
January 2016
November 2020
Table 21 – GAC regeneration at Boughton works at the time of the event. 5 yearly intervals exceeded on GAC1 and GAC5
73 consumers complained to the company and the Inspectorate sent questionnaires to the affected households. A majority of respondents reported that they had stopped drinking the water and five had not restarted using it. Consumers were critical of Severn Trent Water for poor communication during the event with many unable to find information on the company’s website and having to rely on social media or call the company directly for updates. Consumers also reported their frustration in a lack of feedback on the cause of the musty taste with speculation falling on farmers spreading chemicals on the land or a demolished restaurant on the River Dee, neither of which was the cause. Consumers acknowledged text messages sent to close the event but would have appreciated more information on the root cause, the pollutant, and the potential health impacts. The Inspectorate is considering further enforcement of the company for this event.
Companies should learn lessons from this event, in particular the need to keep consumers appropriately informed and the need for prompt and appropriate actions to address water quality risks as soon as possible.
Water safety planning and risk assessment
The Inspectorate’s Risk Assessment team’s function is to understand water companies’ water quality and sufficiency risks, adaptations to new requirements for mitigation and approaches to Drinking Water Safety Planning (DWSP). During 2024 the team assessed large amounts of data and documentation submitted by companies. This information gives the Inspectorate the ability to act and enable companies to comply with regulations 27 and 28 using different types of audits including DWSP audits, individual line assessments of regulation 28 data, and legal instrument closure audits. By making assessments of all the above, the team can progress and maintain risk management practices across the industry. The team also issued guidance where necessary to help companies in their approach to compliance with the regulations regarding risk assessment.
Per and polyfluoroalkyl substances (PFAS)
The Inspectorate has long been aware of challenges related to PFAS, issuing guidance on two specific PFAS, PFOS and PFOA over a decade ago. As the prevalence of PFAS within the environment and scientific advances in understanding their nature and detecting them in water samples has evolved, the Inspectorate has produced further guidance for water companies on the steps required to address PFAS risks. The Inspectorate expects water companies to adopt a tiered approach to risk assessment, monitoring, and management of PFAS concentrations.
PFAS guidance was consolidated and issued in August 2024. It included a requirement to implement a risk reduction strategy to progressively reduce PFAS concentrations at tier 2 as well as tier 3 sites, the application of tiers to final water and raw water where there is no treatment in place, monitoring and reporting of the compound 6:2 FTAB (6:2 fluorotelomer sulphonamide alkyl betaine) added to the list of PFAS parameters and reporting of the ‘Sum of PFAS’.
The latter two requirements were implemented on 1 January 2025, with the expectations of the PFAS guidance extended to companies holding New Appointments and Variations (NAVs). These companies should exchange information and data and also have a forward-looking PFAS strategy. All PFAS chemicals of interest were listed in the Annex C of the Information Direction. It is incumbent on companies to notify the Inspectorate should PFAS chemicals not listed be identified at concentrations above tier 1. The guidance was further updated in March 2025 to provide clarity on company reporting of tier 3 events.
A PFAS and catchment risk assessment working group was hosted by Severn Trent Water at their training academy in Coventry in October. This was attended by industry and regulatory delegates including the Inspectorate. The Inspectorate delivered a presentation on the regulatory perspective of risk assessment in catchments regarding PFAS which reiterated the PFAS guidance issued in August with Information Letter 03/2024. The use of hazardous events to describe potential contribution of PFAS from the catchment within risk assessments was discussed along with the importance of internal and external stakeholder engagement in understanding PFAS risk.
Drinking Water Safety Plan (DWSP) guidance
The World Health Organization (WHO) published an updated Water Safety Plan (WSP) manual in March 2023. During 2024, the Inspectorate worked on revising DWSP guidance to incorporate the approach and continuing endorsement of fundamental components described in the WHO WSP manual. A draft of the new guidance was circulated to members of the Drinking Water Safety Plan Forum to enable companies to give feedback on changes made. The new guidance aims to improve consistency in reporting DWSP data across the industry.
The feedback from the industry included needs for general clarification on wording regarding risk scoring, supporting documents to an overarching DWSP methodology and referencing, inclusion of the hazard ‘quantity’, nitrate/nitrite formula inclusion, hazard groups, regulation 26 turbidity inclusion, PFAS and pesticide reporting requirements and future risks. A working group was convened in December, hosted by Southern Water, where clarification for company queries was documented for feedback. The specific issues regarding hazardous events and a carried forward risk recording method was concluded. The working group also concluded that an annual return of regulation 28 data was not necessary. The upload data from the Inspectorate database shows many risk lines are skipped during the annual submission due to companies reviewing risks throughout the year. Companies may still submit an annual data set if they wish but this will no longer be a requirement following an update to the Information Direction due to be published in 2025.
The Inspectorate added a new category J to account for carried forward risks as part of this guidance and has also mandated the application of categories regarding regulation 27 and 28 notices. Category D must be applied to risks and/or risk lines with control measures identified by any regulation 27 or regulation 28 notice within three months of receiving a notice. Category E must be applied to risk lines for assets identified within regulation 27 and regulation 28 notices or whole company notices where specific parameters or control measures have not been listed, and a review of risks is required, also to be applied within three months of receiving a notice.
The Information Direction, published in July 2024, incorporated regulation 28 reporting specifications. This enabled better tracking of the reporting requirements for the industry and separates DWSP guidance from the requirements for provision of information.
Audits
The Inspectorate continues to highlight recurring themes across all DWSP audits undertaken to date, including the variability and inconsistency of recording of risks across the industry and a continuation of reactive rather than proactive drinking water safety planning. Companies must move towards improved DWSP processes that proactively protect public health and ensure compliance for regulatory parameters rather than only maintaining a DWSP approach in retrospect of water quality or quantity issues.
The majority of DWSP audits to date have resulted in ‘minded to enforce’ and/or legal instruments being issued to review regulation 27 risk assessments and regulation 28 reporting. The new DWSP guidance should address some of the inconsistencies we have identified throughout the year and improve the quality of the information provided.
During 2024, the risk assessment team carried out four audits on the drinking water safety plans at Portsmouth Water, Southern Water, Dŵr Cymru and Northumbrian Water alongside Inspectors from the regional teams within the Inspectorate.
Portsmouth Water – Following a review of the company’s regulation 27 notice, it was identified that there were outstanding actions required to comply with the requirements of the notice. The company continues to work on surface water catchment risk assessments required to satisfy the requirements of the notice.
Southern Water – The Risk Assessment team undertook a two day audit which comprised a day to assess the company’s DWSP, and a technical site audit at Findon water treatment works and Tenants Hill service reservoir. A number of deficiencies were identified with the DWSP, the main areas highlighted included that although there was sufficient knowledge of risks within the company, this was not always reflected in the DWSP. There was a requirement for the company to produce an overarching methodology rather than rely on several separate documents which should be referenced within the methodology. The company demonstrated a lack of proactive risk assessment resulting in the company not proactively assessing all the company risks to drinking water supplies, and a strong reliance on sample results alone to identify risks. Other areas of concern included a lack of procedure around interpretation of bulk supply incumbent risk scores.
Dŵr Cymru – A two day DWSP audit including a review of disinfection policy at Bryn Cowlyd works and a site visit to Pyllau service reservoir, resulted in a regulation 27 ‘minded to enforce’ letter. Whilst the staff present at the audit appeared to have a good understanding of the technical areas within the DWSP, a number of recommendations were made around the company methodology. These included the requirement to include details on how bulk supplies are risk assessed, definition of the assets and stages included in the DWSP process as well as any seasonal variations in assets in service, and information on how the DWSP process is carried out, all of which are fundamental elements of a DWSP. Other areas identified as needing improvements included documenting of training and competence, descriptions for triggers for action on risk identification, and the process for assigning risk scores and DWI categories.
Northumbrian Water – The assessing Inspectorate team were joined by colleagues from the Drinking Water Quality Regulator for Scotland (DWQR) for a two day DWSP audit and technical audit at Mosswood water treatment works and Castleside service reservoir to understand how the company are progressing in delivery of their companywide notice for Hazard Review, developing and implementing their DWSPs throughout the hazard review process and to see evidence of improvements specific to Mosswood works.
The operational staff at Mosswood works and Castleside service reservoir were found to be very knowledgeable of these sites and the company have been commended for this. However, the key findings of the audit identified unacceptable risks associated with clarifier maintenance and wash water supernatant return, both of which present the risk of turbidity impacting disinfection and efficacy of significant barriers for the removal of Cryptosporidium. The audit also found that changes to the disinfection policy were required. As such, the Inspectorate has issued the company with ‘Minded to Enforce’ letters covering the required actions for delivery under legal instruments yet to be determined.
Risk Assessment Record (RAR) reporting and company breakdown of DWI categories
The annual submission of companies’ regulation 28 risk assessment report data took place in October 2024. Companies were able to use the online portal for the 2024 submission including uploading of their DWSP methodologies and declaration with Director sign off. There are occasionally issues with new processes for data submissions, however any problems were easily resolved with good communication from companies and input from the Inspectorate’s Data Team.
Risk assessment record data is submitted using the DWI categories shown with definitions in the table below. Companies must apply DWI categories appropriately to allow data to be meaningful and to give clarity in risk management. The Risk Assessment Risk Index (RARI) score multiplier is included in the table below along with an indication of whether the number of days a category is in place is considered in the RARI calculation. This shows that, for hazards not yet mitigated and verified (C, D, E), the RARI score multiplier increases a companies’ RARI score for those hazards significantly, dependent on the number of days these categories are in place. See the RARI section below for company scores.
DWI Hazard Category
Description
RARI Score Multiplier
Days in Category used?
A
Target risk mitigation achieved, verified and maintained
0.1
No
B
Additional or enhanced control measures which will reduce risk are being validated
0.5
Yes
C
Additional or enhanced control measures which will reduce risk are being delivered
2
Yes
D
Additional or enhanced control measures are required to materially reduce risk
3
Yes
E
Risk under investigation
4
Yes
F
Partial mitigation
0.1
No
G
Control point downstream
Not included in the calculation
H
No mitigation in place and none required
0.1
No
I
Future risk
Not included in the calculation
J
No mitigation in place, carried forward risk: control point upstream
Not included in the calculation
X
Risk record no longer relevant
Not included in the calculation
Table 22 – DWI RAR hazard categories
The pie chart below shows that over half of the industry identified risks to water quality have verified mitigation in place.
Figure 13 and Table 23 – The percentage of RAR categories across the industry at the treatment stage for England and Wales.
RAR Category
% Category at treatment stage
A
64.80%
B
2.50%
C
3.80%
D
7.80%
E
1.70%
G
0.20%
H
18.50%
I
0.80%
BCDE
15.80%
Risk assessment record categories F, G, I and X have been excluded from the above chart. Category F accounted for 0.18% of treatment stage risks across the industry where there is partial mitigation at this stage, usually these risks are also further mitigated downstream, and companies may use category G to also represent these risks. The percentage of category G risks at treatment works was 0.2%. These risks are typically hazards such as nitrate that can be mitigated by blending downstream of the treatment stage in company distribution systems. Category I risks made up 0.8% of the total risk categories applied at the treatment stage, although the use of this category may increase as the industry expands DWSP and records future risks to water quality and sufficiency of supply. Future risks are also discussed in a section below. Category E has been included in the data described as ‘hazards needing mitigation and validation’, however there may be risk outcomes that demonstrate mitigation is not required.
Hazards with categories C, D and E contribute to high RARI scores over time. As these categories indicate investigations into hazards (E), mitigation being needed (D), and solutions in the delivery phase (C). The longer the categories remain in place during this process, the longer there is a risk of water quality from these hazards. The top ten hazards in the section below show which hazards have the highest percentage of whole industry RARI scores. Category B risks may have had mitigation delivered, reducing the risk to water quality, however, the mitigation now in place for these risks is still being verified. Companies with regulation 27 and 28 notices must retain hazards at category B until the end of such notices, and the Inspectorate is satisfied through company completion reports that any hazards under notice have suitable control measures in place.
Risk Assessment Risk Index
The RARI is dependent on DWI category application to risks perceived by companies. Companies are required to report risk assessments and show where risks are carried forward through supply systems from catchment/source to the consumer tap. Since the introduction of DWI categories, companies have used different methods to show carried forward risks. This is achieved either by using the DWI categories applied at assets with active risks and applying the same categories at downstream assets; or using residual risk scoring to demonstrate risks moving forward through a supply system. As such, RARI values for companies have not been comparable across the industry and can only show changes over time when viewed on an individual company risk profile.
RARI has been reported for companies within the DWI annual reports over the last five years from 2019 to 2023. The index is a useful tool in showing active risks within companies and is being redeveloped as companies implement changes to how DWI categories are applied, gaining a more consistent approach over the next few years. This includes the introduction of a new category ‘J’ for carried forward risks. Although this category will not be included in the RARI calculations, it will allow for a more consistent approach within the industry for category application across company supply systems.
Figure 14 and Table 24 – Top 10 current identified risks to the whole industry
Hazard Name
% Whole Industry RARI
No supply
16.22%
Cryptosporidium oocysts
12.29%
Perfluorooctane Sulfonate
11.95%
Perfluorooctane Acid
11.31%
E. coli
10.76%
Enterococci
9.51%
Total coliforms
7.94%
Lead
7.04%
Clostridium Perfringens
6.65%
Turbidity
6.33%
The top 10 hazards represent 39% of all hazards included in RARI calculations.
Figure 15 & Table 25 – Company average RARI scores for 2023 and 2024 are shown below. The median RARI value is 7.78.
Company code
2023 RARI score
2024 RARI score
NES
11.77
25.20
BRL
17.66
23.56
SVT
5.22
19.22
SWB
12.72
14.94
SRN
8.88
13.16
SST
9.21
12.49
ANH
8.16
11.27
DWR
6.60
9.43
WSX
3.38
6.12
SES
0.53
4.78
CAM
4.82
4.40
YKS
2.96
4.29
TMS
1.79
4.15
SEW
3.18
3.96
UUT
3.17
2.08
LNW
1.60
1.53
AFW
0.29
0.72
IWN
0.57
0.39
ICW
0.44
0.19
ALB
0.18
0.13
ALE
0.07
0.07
Figure 16 & Table 26 – Company average RARI scores for 2023 and 2024 are shown below – graph 2
Company code
2023 RARI score
2024 RARI score
ISC
643.51
2110.28
ESP
38.68
184.58
VWP
746.85
169.41
PRT
272.78
129.67
HDC
117.43
47.43
RARI scores have increased for 15 out of the 26 companies shown in the above figures between 2023 and 2024 as the industry has increased hazard identification and recording of risks. This is likely to be the case over the AMP8 period through improvements made to hazard identification processes. These improvements may be implemented through Inspectorate legal instruments issued to companies and/or development of approaches in line with newly published DWSP guidance. Companies must implement changes to recording and reporting risks in line with the Information Direction 2025 by February 2027.
AMP 7 RARI trends
The RARI trends across the AMP7 period shown below are indicative of where the Inspectorate expects companies to be. As companies continue to identify and record risks in their DWSPs, an increase in RARI scores is inevitable, as observed in 2023 and 2024. The Inspectorate expects to see company RARI scores vary over time as risk identification is improved and solutions to mitigate risks are delivered, downward trends will follow over future AMP periods as companies work through PR24 schemes and legal instruments. The rates of change in RARI scores will vary between companies as each has their approach to DWSP linking to investment plans and timescales for delivery of any control measures needed to reduce water quality risks.
Whole Industry AMP7 RARI Table
Company
2020 RARI
2021 RARI
2022 RARI
2023 RARI
2024 RARI
ISC
–
–
519.561
643.51
2110.3
ESP
–
–
190.06
38.684
184.58
VWP
–
–
101.529
746.85
169.41
PRT
9.58
13.20
31.01
272.78
129.67
HDC
39.198
72.352
124.830
117.43
47.425
NES
0.42
1.28
1.60
11.77
25.20
BRL
13.08
6.47
4.63
17.66
23.56
SVT
5.58
10.10
5.15
5.22
19.22
SWB
1.22
2.95
13.27
12.72
14.94
SRN
2.98
3.34
5.31
8.88
13.16
SST
0.75
2.78
7.41
9.21
12.49
ANH
4.00
7.85
3.23
8.16
11.27
DWR
1.533
2.015
2.864
6.6
9.434
WSX
0.48
0.54
1.82
3.38
6.12
SES
0.13
1.67
0.21
0.53
4.78
CAM
0.07
0.05
8.95
4.82
4.40
YKS
2.53
1.41
0.74
2.96
4.29
TMS
1.32
1.36
1.62
1.79
4.15
SEW
1.36
1.67
5.40
3.18
3.96
UUT
1.40
2.93
4.12
3.17
2.08
LNW
1.89
5.68
3.11
1.60
1.53
AFW
0.39
0.68
1.14
0.29
0.72
IWN
1.64
1.00
0.85
0.57
0.39
ICW
0.50
0.85
0.42
0.44
0.19
ALB
0.23
29.41
0.18
0.18
0.13
ALE
–
–
0.07
0.07
0.07
Table 27 – AMP7 RARI scores
Portsmouth Water and Hafren Dyfrdwy RARI trends are shown on the primary axis in the graph below [Figure 17] for scale alongside companies with similar trends. Both companies have had high RARI scores over the last few years described below.
Hafren Dyfrdwy included risks identified through notices served in 2022 to their DWSPs, including a regulation 28 notice on individual service reservoirs and affected supplied zones, and a notice for concessionary supplies and installation of large water mains to supply areas north and south lake Vyrnwy. As the company has made good progress with delivery of solutions under these notices, this is shown by a decreasing trend in their RARI scores from the middle of AMP7 to present.
Portsmouth Water was served a regulation 27 notice for catchment risk assessment and a management and training regulation 28 notice served in 2021, leading the company to identify and record these risks in their DWSPs shown by an increase in RARI from 2022 to 2023. The company continues to be on target with delivery against these notices indicated by a decrease in their RARI scores across their supply systems from 2023 to present.
Cambridge Water and United Utilities show similar trend profiles across AMP7 with RARI scores increasing during 2021 to 2022, followed by a decline in scores to 2023 as delivery of solutions conclude during 2025 and early 2026.
Figure 17 & Table 28 – Companies with RARI scores >10 at the end of 2024 are shown below.
Companies shown in the graphs below show similar increases in RARI scores at the start of AMP7 to those in Figure 17 above, however further increases have followed from 2022 to present due to other legal instruments served during the AMP period and updates to ongoing notices for AMP7 continuing into the AMP8 period.
Figure 18 & Table 29 – Companies with RARI scores <10 at the end of 2024 are shown below.
Company
2020 RARI
2021 RARI
2022 RARI
2023 RARI
2024 RARI
DWR
1.533
2.015
2.864
6.6
9.434
WSX
0.48
0.54
1.82
3.38
6.12
SES
0.13
1.67
0.21
0.53
4.78
CAM
0.07
0.05
8.95
4.82
4.40
YKS
2.53
1.41
0.74
2.96
4.29
TMS
1.32
1.36
1.62
1.79
4.15
SEW
1.36
1.67
5.40
3.18
3.96
UUT
1.40
2.93
4.12
3.17
2.08
ALB
0.23
29.41
0.18
0.18
0.13
NAV RARI score changes across AMP7 are shown below. The figure excludes ESP Water, Veolia Water Projects and Albion Eco. Albion Eco continues to have a RARI score of 0.07 for the one site it is responsible for at Shotton Mill. ESP Water and Veolia Water Projects data are shown in the whole industry AMP7 RARI table above.
Figure 19 and Table 30 – AMP7 RARI trends for NAV companies
Company
2020
2021
2022
2023
2024
LNW
1.89
5.68
3.11
1.60
1.53
IWN
1.64
1.00
0.85
0.57
0.39
ICW
0.50
0.85
0.42
0.44
0.19
Future risks
Seventeen companies use category ‘I’ indicating their individual perceived future risks that may need to be investigated and mitigated. Such risks include hazards that may be associated with emerging contaminants, climate change, changes in raw water quality and sufficiency, and asset condition and longevity. These risks are not necessarily manifesting now, but companies are keeping a watching brief over them. The top ten hazards where category I has been used in company submitted regulation 28 data is shown below.
The graph below shows that the highest proportions of company perceived future risks are from abstraction and storage stages.
Figure 20 and Table 31 – Top 10 future risks
Hazard Name
% of total future risk
Nitrate
7.03%
No supply
6.28%
Total coliforms
2.22%
Per- and polyfluoroalkyl substances (PFAS)
2.02%
Iron
1.79%
E. coli
1.72%
Cryptosporidium oocysts
1.49%
Turbidity – indicator
1.38%
Clostridium Perfringens
1.27%
Lead
1.25%
Examples of these risks included single source contamination associated with nitrate risk, structural integrity of service reservoirs leading to a sufficiency of supply risk, and degradation of internal structures of boreholes causing a risk of iron in the raw water source supplied.
Perfluoroalkyl and polyfluoroalkyl substances (PFAS)
Perfluoroalkyl and polyfluoroalkyl substances (PFAS)
PFAS are a group of man made compounds, the basis of which are chains of carbon and fluorine atoms. They contain at least one fully fluorinated methyl or methylene group. The carbon-fluorine bond is very strong and so these compounds do not degrade easily in the environment. They are resistant to grease, oil, water, and heat and so they have found a large range of uses, for example, in stain and water-resistant fabrics and carpets, as well as in paints and firefighting foams, cookware, and food packaging.
The production of these substances, their use in products and their use and disposal means that they are now being found widely in the environment throughout the world. Ultimately, because of the persistence of the substance they are eventually found in water, be that groundwater or surface water.
In August 2024 the Inspectorate updated its guidance to the industry regarding requirements to submit sample results and summary risk assessment information for PFAS, this remains a major focus. Companies have continued with their targeted sampling strategy to focus on those sites which are likely to be at risk from PFAS contamination. In 2024 companies collectively carried out over 770,000 analyses for individual PFAS, and in total, over 1.7 million analyses have been performed since 2012, providing a significant dataset to understand the challenges in drinking water.
PFAS tiers are now applied to any PFAS chemicals of interest detected in the final or raw water. Sites are classified as:
Tier 1 where PFAS concentrations are <0.01 µg/L;
Tier 2 where PFAS concentrations are <0.1 µg/L; and
Tier 3 where PFAS concentrations are ≥0.1 µg/L.
PFAS tiers are to be applied to all PFAS chemicals of interest identified in the parameter list (Annex C of the Information Direction) detected in final water. The latest guidance on the actions companies should be taking for the three tier levels is available in our most recent guidance – DWI_PFAS-Guidance_Mar_2025.pdf
Monitoring by water companies has highlighted a further PFAS compound of potential concern; 6:2 fluorotelomer sulfonamide alkylbetaine (6:2 FTAB). This compound has been added to the parameter list and companies are expected to initiate monitoring and reporting for this parameter as soon as practical.
Companies are also expected to consider the effect of combined concentrations of the PFAS chemicals of interest identified in the parameter list. As such, the requirement to implement a prioritised mitigation methodology to progressively reduce PFAS concentrations in drinking water has been further extended to include combined PFAS on a ‘sum of’ basis. Companies have now implemented reporting for the ‘sum of PFAS’ based on the 48 named PFAS compounds in the parameter list. Where sites now fall into tier 2 or 3 for the sum of parameter these sites should be rolled into the existing site prioritisation approach based on their relative classification and an appropriate risk reduction strategy should aim to progressively reduce PFAS concentrations in drinking water.
The analysis targets the source water because this provides information on the hazard and informs the necessary mitigation required, be that blending, removal of the source water or treatment. During 2024 there were no samples reported in tier 3 for any treated water being supplied to consumers. In total 351 samples taken from raw water abstractions had results within tier 3. This helps to demonstrate that the current industry strategy of mitigating the risks from PFAS is working effectively to protect consumers. 96% of the samples taken were less than the detection limit for their analytical methodology.
Tier
Raw water tests
Treated water tests
Total
Tier 1
287,840
413,084
700,924
Tier 2
28,888
17,223
46,111
Tier 3
351
0
292
Total
317,079
430,307
747,386
Table 32 – Number of tests in 2024 within tiers including results less than the limit of detection
The most prevalent species in raw water during 2024 is PFOS 21.1% of all positive sample results, the below table sets out all the other parameters which contributed greater than 1% of detections by number of samples rather than by result for all tiers.
Raw water data – number of tests per tier greater than the limit of detection (LOD)
Parameter
Tier 1 >LOD
Tier 2 >LOD
Tier 3 >LOD
Total >LOD
PFOS
1,499
541
74
2,114
PFHxS
1,254
428
25
1,707
PFOA
1,603
93
7
1,703
PFHxA
1,405
197
15
1,617
PFBS
1,476
49
2
1,527
PFBA
1,223
46
1,269
PFPA
821
200
15
1,036
PFHpA
883
10
14
907
Sum_of_PFAS
392
132
36
560
PFecHS
216
122
338
PFPS
264
32
3
299
FBSA
206
12
7
225
6:2 FTAB
189
29
3
221
6:2 FTSA; 6:2 FTS
97
84
13
194
PFDA
193
1
194
FHxSA
134
49
10
193
PFHpS
123
13
136
8:2 FTSA
115
9
124
HFPO-TA
115
115
PFNA
115
115
PFUnDA
111
111
EtFOSAA
103
103
MeFOSAA
92
92
PFNS
92
92
FOSA
82
9
91
HFPO-DA (Gen X)
82
82
PFDS
81
81
PFDoDA
79
79
PFHxDA
78
78
PFODA
78
78
PFTeA
78
78
11Cl-PF3OUdS
77
77
NFDHA
75
75
EtFOSA
74
74
PFTrDA
74
74
4:2 FTSA
72
72
MeFOSE
72
72
PFEESA
72
72
3:3 FTCA
71
71
DONA
71
71
PFDoS
71
71
5:3 FTCA
2
68
70
PFMOPrA
70
70
PFMOBA
69
69
PFUnDS
69
69
7:3 FTCA
68
68
MeFOSA
68
68
EtFOSE
63
63
9Cl-F3ONS
34
34
Total
14,451
2,056
292
16,799
Table 33 – Raw water PFAS data
Treated water data – number of tests per tier greater than the limit of detection (LOD)
Parameter
Tier 1 >LOD
Tier 2 >LOD
Total
PFBA
2,939
75
3,014
PFHxA
1,943
361
2,304
PFOS
1,493
214
1,707
PFBS
1,489
14
1,503
PFPA
1,058
384
1,442
PHFHxS
1,135
167
1,302
PFOA
1,068
57
1,125
PFHpA
698
698
6:2 FTSA; 6:2 FTS
84
367
451
Sum_of_PFAS
154
51
205
6:2 FTAB
98
8
106
PFPS
106
106
PFDA
86
86
FBSA
70
70
FHxSA
40
22
62
PFHpS
53
53
PFecHS
41
8
49
8:2 FTSA
43
1
44
PFNA
36
36
NFDHA
31
31
FOSA
28
28
PFUnDA
27
27
PFNS
25
25
9Cl-F3ONS
22
22
EtFOSAA
14
14
MeFOSAA
14
14
PFEESA
14
14
PFDoDA
11
11
PFDS
8
8
PFTeA
8
8
11Cl-PF3OUdS
7
7
HFPO-TA
5
5
MeFOSE
2
2
EtFOSA
1
1
PFHxDA
1
1
PFMOBA
1
1
PFODA
1
1
PFUnDS
1
1
Total
12,855
1,729
14,854
Table 34 – Treated water PFAS data – zero tier 3 detections in 2024
Affected sites
Where PFAS is identified, action is taken by the company in line with the risk prioritisation strategy. For instance, in 2022, there were two tier 3 results from the outlet point of water treatment works, which were subsequently blended within the distribution network to reduce levels to well below the tier 1 threshold prior to supply to consumers. In 2024, no samples were within tier 3 for treated water. Whilst no tier 3 detections occurred within 2024, similar action will be taken in the future to ensure the continuing protection of public health and consumer confidence should there be any further tier 3 detections, including the ‘sum of PFAS’ for the 48 named parameters.
For the PFAS sampling the company undertakes risk based sampling which is specifically focused on the assets most at risk of failing, therefore the number of samples in tier 2 might look high but these are taken from a small number of sites. Therefore out of 1067 treatment works in supply across England and Wales in 2024 tier 2 samples were detected at only 46 locations – 4.3%.
Company name
Count of Sample Result in tier 2
Actual number of affected sites
Affinity Water Ltd
266
7
Anglian Water Services Ltd
1097
16
Bristol Water Plc
24
2
Isles of Scilly
4
1
Northumbrian Essex and Suffolk water
6
2
SES Water
3
1
Severn Trent Water Ltd
3
1
South Staffordshire Water Plc
43
6
Southern Water Services Ltd
240
2
Thames Water Utilities Ltd
8
4
United Utilities Water Ltd
2
1
Wessex Water Services Ltd
33
3
Table 35 – number of sites affected by PFAS Tier 2 results
Audit programme completed by the Inspectorate
In 2024 the Inspectorate carried out 77 audits, this is an increase over the 43 carried out in 2023 and highlights the Inspectorates increased focus given on water companies. The audits comprise of a mixture of onsite inspections, focused whole company audits and remote vertical audits.
The Inspectorate carries out series of thematic audits designed to access performance across the industry to look for areas of good and poor practice to disseminate the learning from these inspections widely across the industry to enable poorer performing companies to learn from examples of good practice.
Figure 21 & Table 36 – Number of audits per year since 2018
Year
Number of audits
2018
76
2019
38
2020
90
2021
56
2022
51
2023
41
2024
71
Featured audits
Severn Trent Water – Bottle Store
Bottled water supplied by water companies is subject to the same regulations as water supplied by pipes or tankers and the storage. Additionally, bottled water must be treated like a food product considering the additional risks of the environment in which it is stored and the protection of the bottles if they are plastic as this could be affected by heat, sunlight, and rodents or other wildlife which may destroy or degrade the plastic or contaminate the bottle tops.
The Inspectorate conducted an unannounced audit of the bottled water kept at a Severn Trent Water storage facility on 27 September 2024. The storage facility was on first sight, unhygienic, and as a result the Inspectorate had no choice but to intervene to ensure that all the stored water was quarantined and destroyed to prevent its supply to consumers.
Figure 22 – Bottle storage facility
The storage facility was a dilapidated asbestos clad warehouse on a non-operational service reservoir site. It had been repurposed for bottled water storage in September 2021. The roof and walls were damaged, and skylights exposed the stored water to direct sunlight.
Figure 23 – Damaged roof
Figure 25 – Damaged walls
Figure 24 – Asbestos warning signs
The doors to the facility were inoperable and at some stage an attempt had been made to place a tarpaulin cover over the entrance way. However, at the time of the audit the tarpaulin was pulled back from the doorway and held down by old pallets to prevent it from blowing in the wind. There is no evidence that this temporary cover was ever extended to the full height of the opening. The tarpaulin cover was dirty and covered in bird faeces.
Figure 26 – Poor condition of the dirty tarpaulin cover at the entrance
Severn Trent Water reported that concerns about the asbestos and leaking roof had been raised in December 2021 and that verbal reports of difficulties with operating the doors had been ongoing since late 2022, but the company were unable to provide any evidence of these concerns being raised, nor that any action was being taken to address the unsatisfactory storage conditions and exposure to the outside elements. Nevertheless, the exceptionally poor condition is evident as can be seen in the photo’s
Internally the facility was found to house approximately 300 pallets stored from wall to wall and covered in plastic sheeting. The top of the sheeting was covered in faecal material and the underside in contact with the pallets of bottles was dirty, suggesting it had been resting on the floor at some point.
Figure 27 – Covering on the pallets of bottles
Figure 29 – Environmental contamination
Figure 28 – Faecal contamination
Many of the pallets of bottles still had the plastic covering from the supplier and this was seen to be dirty but remained intact. The Inspectorate discovered an open pallet with dirty bottles, from which a number had been taken and are likely to have been supplied to consumers. However, the company did not maintain records that could confirm where the missing bottles were sent.
Figure 30 – Dirt on the packaging
Figure 33 – Opened pallet
Figure 31 – Wet floor (source unknown)
Figure 32 – Filthy flooring
The floor of the warehouse was wet with the source either from the bottles or the environment that they were kept in. This could not be determined on the day. The floor was generally filthy and covered in faecal material.
Severn Trent Water reported that concerns with the facilities were raised internally on 5 September, about 3 weeks before the Inspectorate’s visit. The company had inspected the site on 13 September and had decided that the site was not to be used until further notice. The delay of over a week could have resulted in further deployments from the site in the interim. The company had taken no steps to visibly quarantine the stock at the time of the Inspectorate’s visit but subsequently erected a flimsy sign by the broken door to advise staff not to use the facility. The access was not even barriered off to prevent entry. This is not a drinking water quality first approach.
Figure 34 – Signage erected following the Inspectorate’s visit
By storing the pallets from wall to wall, there was little opportunity for stock rotation and given the access limitations to the rear of the facility the Inspectorate were unable to confirm the age or batch numbers of the bottles stored at the rear of the warehouse. However, from the records available the warehouse was restocked in June 2024 following the deployment of 200 pallets of water to another company via a mutual aid agreement. The company were unable to confirm the batch numbers of the bottles supplied, the traceability of the stock was deficient. Evidence suggests that the bottled water had been stored for approximately 18 months, prior to the mutual aid request and most likely in the poor conditions observed in September 2024.
The company has a procedure that requires monthly sampling of stored bottled water, however for the batch deployed via mutual aid records for February and March 2024 only were available. The results were satisfactory for taste/ odour and routine microbiological parameters.
Following the audit the Inspectors concluded the lack of documented procedures, records and escalation of the issues, including the disregard for the presence of faecal material, poor environment of the storage facility, including inoperable doors and damaged asbestos storage facility, seriously undermines the Inspectorate’s confidence in the training and culture of the network response team responsible for the facility, and the inadequate response to quarantining and disposal of the poorly stored water perhaps raises doubt in the wider water quality culture within the company.
The complacency of the network response team and company to remediate the identified issues resulted in the deterioration of the facility with the conditions considered inadequate by the Inspectors for the storage of water intended for consumption and non-compliant with the industries own technical guidance note 11 concerning the storage and use of bottled water.
The Inspectorate took prompt action to serve a provisional enforcement order (PEO) on the company prohibiting the supply of any water from the store and to ensure its destruction. This is the first occurrence where such action has been necessary by the Inspectorate and is disappointing that this was necessary.
The company has discontinued using the facility with alternative third party storage locations now used for bottled water storage. Severn Trent Water also committed to further training of its staff with respect to management of bottled water in response to the provisional enforcement order.
The Inspectorate made recommendations for the company to improve procedures and implement an appropriate system of water hygiene audits for bottled water storage facilities.
A recommendation was also made for the company to consider the quality of bottled water supplies as part of its regulation 27 risk assessment and for this evidence of this in its reports.
There may be an assumption within the industry that bottled water is always stored hygienically. This incident shows that this is not always the case. The Inspectorate expects all companies to consider the water quality risks associated with bottled water supplies and ensure that it has appropriate training, procedures, and inspections in place to ensure action is taken to maintain hygienic supplies of bottled water as required. Similar audits may well be necessary across the industry to provide assurance that there are no similar situations.
Northumbrian water – Mosswood works audit
When a company notifies the inspectorate of an event which is considered sufficiently serious or there are repeat occurrences which may indicate a changing risk profile for a site, an audit may be carried out to determine the facts because drinking water is a critical societal service which can have a public health impact. One such occasion arose when there were two notifiable events in 2024 at Northumbrian Water’s Mosswood works following a power interruption. The lack of generator power led to treatment issues and sub-optimal clarification on two separate occasions in July and August 2024. The impact of a loss of power can be far reaching not just in the loss of supply but more critically the loss of some treatment processes but water is still in supply creating the risk of improper treated water reaching consumers.
Further to these events, an event was retrospectively notified, in August, due to a potential regulation 26 breach, that means preparing water sufficiently for disinfection following filter media replacement, and a return to service of the site. Retrospective notifications usually arise because a company either doesn’t think the threshold has been met for a notification, internal communications to water quality have not occurred so those responsible for making a notification don’t know, or the Inspectorate identifies information upon which a company is informed that they must notify.
As a third issue, the works had two coliform detections in regulatory samples in 2024. The company attributed the first detection in January 2024 to deficiencies with the sampling facilities, and the second in August 2024 to the condition of the contact tanks. Both contact tanks were inspected in 2023 and the company were given a recommendation to inspect them again following the first coliform detection in January 2024. ROV inspections were carried out in July 2024 where minor ingress was found in both tanks and some sediment deposition on the tank floor. The ingress in one tank was repaired, but investigations on the route of ingress in the other tank did not find the source. As a result, the company committed to installing a roof membrane over both tanks to mitigate the risk of ingress.
Given the ongoing concerns, the works was understandably subject to an audit by the Inspectorate in November 2024. In addition to the technical audit, a risk assessment and disinfection policy audit was carried out. The Inspectorate made recommendations around the filter monitoring and performance and hypochlorite dosing, specifically the chlorine residual and effective contact time to ensure disinfection is consistently achieved because of the long loop times and lack of chlorine residual monitoring. Furthermore, issues with works flow control, monitoring, and recirculation to the head of the works in contravention to the recommendations within the Badenoch and Bouchier expert report on Cryptosporidium were also found during the technical audit.
Figure 35 – Site trend showing excessive levels of turbidity being recycled to the head of the works
The risk assessment audit found good processes in place; however, the Inspectorate gave recommendations around the drinking water safety planning (DWSP) methodology. Further recommendations were made regarding the deficiencies identified around the DWSP training for the wider business and lack of internal auditing/verification processes for the DWSP.
The company’s disinfection policy was also reviewed as part of the audit, during which several deficiencies were identified. These included gaps in policy, training, insufficient alignment between the general policy and the site-specific disinfection policies (SSDP), lack of detail on disinfection approaches, discrepancies between SCADA Ct calculations and those outlined in the SSDP, and inconsistencies with relevant standards. As a result, the company was issued with a regulation 28(4) notice.
The audit identified multiple critical deficiencies across operational control, disinfection practices, and risk management. While some good processes were in place, the Inspectorate reminds water companies of the importance around filter management and flow monitoring, chlorine dosing and validation, correct operation of the recirculation to the head of the works, and DWSP implementation and training because together the risk incrementally increases. The Inspectorate expects water companies to establish a concise disinfection policy framework that is underpinned by robust scientific principles and can be adapted to site-specific requirements to protect public health.
Southern Water – Brede works audit
In addition to responsive audits, such as that exampled above, audits are also undertaken on a random basis to verify the general state of treatment works and supply systems which may otherwise not receive a visit or as an ongoing check on progress with any existing enforcement. Brede is one such example where the audit was to assess the works as part of the Inspectorate’s surface water treatment works audit programme for the third quarter of 2024, and to assess progress against legal instrument
Brede works is a surface water site treating water from Powdermill and Darwell surface water reservoirs and four interconnected wells. There were a number of recommendations surrounding critical treatment processes which were suboptimal. These were for the company to investigate and implement methods to ensure coagulant dose and DAF performance is optimised; to rectify the shortfall in media replacement which had not been corrected for six years; to investigate the settlement time following filter backwash which was recorded by the company to be 10 minutes long; to investigate the cause of the recurrent Clostridium perfringens detections and to develop robust short and long term solutions to reduce the risk of further detections. Further recommendations were made against filter performance, operation, inspections, primary filter roof repair and planned maintenance to clean the filter lauders. In the long term, the Inspectorate recommended replacement of the filters with a more appropriate and robust solution.
Figure 36 – Sodium hypochlorite dosing bund, the cause of the chlorate event and the reason for visiting the works
The Inspectorate found the works’ final water turbidity alarm allowed water to enter the final stage of disinfection for 30 seconds at a turbidity greater than 1 NTU before allowing the works to shut down. A recommendation was made to the company to introduce an appropriate alarm to allow works shutdown before the requirements of regulation 26 are breached at this site. The requirement to prepare water for disinfection by ensuring turbidity is below 1 NTU has been a requirement since 2007, it is therefore concerning that example of non-compliance with this requirement are still identified. The Inspectorate reminds all companies that water with a turbidity of greater than 1 NTU entering the final point of disinfection is in breach of the Regulations and all precautions must be taken to mitigate this scenario. Brede works is currently subject to an improvement notice, however the Inspectorate was minded to initiate further enforcement action following the audit.
South East water – Hazards Green works
Also in October 2024, the Inspectorate also visited South East Water’s Hazards Green works. The works is a surface water works located in East Sussex. Water is abstracted from the Wallers Haven River, Darwell Reservoir (which is managed by Southern Water) and an onsite well. South East Water list media depth checks for filters as a control measure on the company regulatory risk assessment however at Hazards Green works, it was apparent this was not taking place. This is a vital critical control measure to ensure filter performance to mitigate against Cryptosporidium breakthrough, highlighted by the Badenoch report of 1990. These finding should not still be identified by audit 35 later. The Inspectorate recommended the company reviews all sites to ensure that media depth checks are being completed at the required frequency and that the company update its Drinking Water Safety Plans to reflect the work it has identified to improve the control monitoring systems at the site.
Anglian water – Pitsford works
In November 2024, the Inspectorate carried out an audit at Anglian Water’s Pitsford works, which is a large surface water site located in Northampton, supplied by the River Nene, Pitsford Reservoir and Holcot, Walgrave and Scaldwell Brooks. The most significant challenge at the works is from pesticides, for which there is Granular Activated Carbon (GAC) treatment in place.
During the audit, Rapid Gravity Filter (RGF) 1 and 8 were found to be drained down and out of service for filter nozzle replacement. A subsequent data request following the audit found that RGF1 had been out of supply since April 2021 and RGF8 since May 2022 as the company had not been able to procure approved nozzles. The Inspectorate was critical that the status of the remaining six filters was being impacted by the company’s passivity in addressing the refurbishment issue and it was recommended that the company remediate the filter issues on site as a priority, so that the requirements of regulation 4 are not impacted in the future.
A further recommendation was made to review how the company’s maintenance systems highlighted instrument calibration dates in response to a turbidity instrument not receiving a timely two-year full loop calibration over a four-year period between 2020 and 2024.
United Utilities – Huntington and Sutton Hall works
In November 2024, the Inspectorate also audited United Utilities’ Huntington and Sutton Hall works, following a taste and odour event on the River Dee, which is the source water for both works.
The Inspectorate requested a Process Controller to be present during the two-day audit however, contrary to expectations, this did not occur. Water companies are under a primary duty to provide all such assistance and provide all such information as reasonably required, not to do so could be considered an offence. The Inspectorate reminds companies that it is always beneficial to have competent, trained and informed site operators present during a works audit to answer any questions regarding the day-to-day operation of the site.
Seven recommendations were made in total, with several under regulation 27, including to update the site risk assessments with site specific control measures; to develop a procedure and process to regularly verify the powdered activated carbon (PAC) dose at both Huntington and Sutton Hall works; to implement regular cleaning of all clarifiers and clarifier inlet channels at Huntington works due to the significant build-up of floc and sludge; to implement better control measures, to prevent contamination from buffers and reagents; and for regular maintenance and cleaning to be undertaken on the Actiflo streams at Sutton Hall works.
Enforcement has been initiated under regulation 28(4) at both sites for shortcomings in the PAC dosing, filtration maintenance and management, and contact tank inspection philosophy at Huntington works and for deficiencies in the PAC dosing system and filtration management at Sutton Hall works.
Affinity water – Kingsdown works
The Inspectorate audited Affinity Water’s Kingsdown works and found the company had not reported compliance data for the pesticides aldrin, dieldrin, heptachlor and heptachlor epoxide in recent years. A recommendation was given to the company to ensure compliance with the general provisions for monitoring in regard to the four aforementioned pesticides at this works and across the company’s estate. Another recommendation was made to ensure samples from Kingsdown works are always representative of water leaving the works as required by regulation 16, since the final water sampling tap had the possibility of being supplied by the network rather than the works, if the works was not pumping in to supply.
Further recommendations were made including the inclusion of sewer pumping stations within the catchment risk assessment; to review the company risk assessment records for risks associated with generators and transformers to be considered and updates to the regulation 28 report to be applied; to ensure risks associated with chlorate are controlled; and to hygienically seal an observation borehole located in close proximity to the site operational borehole.
The Inspectorate’s risk-based audit programme at works has emphasised many recurrent themes across the industry, particularly with regards to inadequate filter performance and maintenance, site-wide risk assessments and general site maintenance. Optimal filter performance and filtration are critical components of the production of a safe and high-quality water supply. However, at the majority of the sites audited, filter performance was found to be sub-optimal, with deficiencies observed in routine maintenance, inspection, cleaning and timely remedial interventions. Continuous risk assessment of treatment works should inform timely updates to company risk assessment reports with appropriate short-, medium- and long-term mitigation and control measures in place. However, this was also found to be inadequate at some of the works that had been audited. Site maintenance was also overlooked at almost all the works audited, in some cases for years, leaving assets to deteriorate.
The Inspectorate will always recommend or initiate enforcement to ensure compliance with the regulations n order to maintain wholesome water supplies to the public.
Enforcement, transformation and recommendations
The Inspectorate publishes the drinking water quality legal instruments on the website under company improvement programmes. Security (SEMD and NIS) legal instruments are considered sensitive and therefore are not published in the public domain. A summary of the legal instruments issued in 2024 is below.
Type of legal instrument
Number of legal instruments
Companies
Regulation 27(4) Notice for improvements to water safety plans
5
Independent Water Networks (1), Leep Networks Water (1), Portsmouth Water (1), South East Water (1), Thames Water (1)
Regulation 28(4) Notice relating to risks identified in water safety plans
34
Northumbrian Water (3), Severn Trent Water (13), South East Water (3), Southern Water (6), South Staffordshire Water (1), South West Water (3), Thames Water (2), United Utilities (1), Wessex Water (1), Yorkshire Water (1)
Enforcement Order under section 18 of the Water Industry Act 1991
2
Severn Trent Water (1), Southern Water (1)
Undertaking accepted under section 19(1) of the Water Industry Act 1991 for drinking water quality improvements
2
Castle Water (1), Wessex Water (1)
Undertaking accepted under section 19(1) of the Water Industry Act 1991 for SEMD improvements
4
Southern Water (1), South East Water (1), South West Water (1), Thames Water (1)
Regulation 17(1) Notice for improvements under the Network and Information Systems Regulations 2018
1
Affinity Water (1)
Regulation 15 Notice for the provision of information under the Network and Information Systems Regulations 2018
2
Affinity Water (1), South Staffordshire Water (1)
Table 36 – Non-PR24 Related Legal instruments issued in England, in 2024
The individual legal instruments listed above have been discussed in detail, within the quarterly Chief Inspectors reports published throughout 2024.
2024 saw the majority of our work to secure legal instruments for the delivery of improvement programmes committed to by companies during PR24, reflected in the large number of legal instruments summarised in the table below. These legal instruments enable us to monitor the progress of company plans to address drinking water quality, NIS or SEMD risks. In their PR24 determination, Ofwat have linked the price control deliverables for enhancement schemes to the DWI issued legal instruments. We shall continue to work closely with Ofwat and keep them updated throughout the AMP. This is the first time that DWI has taken a role in respect of NIS and SEMD at a price review. Our intention was to mirror, as closely as possible, our approach to drinking water quality. As such, we also issued legal instruments for these areas of activity. We were pleased with the overall positive engagement from companies in what was a new approach for all of us. We will seek to continue to guide and support companies through the lifetime of the legal instruments, whilst not losing sight that they are in place to, and our role with them, is to hold companies to account and ensure they deliver on their commitments.
Type of legal instrument
Number of legal instruments
Companies
Regulation 28(4) Notice relating to risks identified in water safety plans
78
Anglian Water (17), Northumbrian Water (3), Portsmouth Water (4), SES Water (2), Severn Trent Water (5), South East Water (6), Southern Water (7), South Staffordshire Water (3), South West Water (14), Thames Water (4), United Utilities (7), Wessex Water (5), Yorkshire Water (1)
Enforcement Order under section 18 of the Water Industry Act 1991
2
Thames Water (2)
Undertaking accepted under section 19(1) of the Water Industry Act 1991 for drinking water quality improvements
29
Affinity Water (2), Anglian Water (2), Northumbrian Water (2), Portsmouth Water (2), SES Water (2), Severn Trent Water (3), South East Water (2), Southern Water (2), South Staffordshire Water (2), South West Water (2), Thames Water (2), United Utilities (2), Wessex Water (2), Yorkshire Water (2)
Undertaking accepted under section 19(1) of the Water Industry Act 1991 for SEMD improvements
19
Affinity Water (2), Anglian Water (2), Northumbrian Water (1), SES Water (4), Severn Trent Water (2), South East Water (1), Southern Water (2), South Staffordshire Water (1), South West Water (1), United Utilities (1), Yorkshire Water (2)
Regulation 17(1) Notice for improvements under the Network and Information Systems Regulations 2018
15
Affinity Water (1), Anglian Water (1), Northumbrian Water (1), Portsmouth Water (1), SES Water (1), Severn Trent Water (1), South East Water (1), Southern Water (1), South Staffordshire Water (1), South West Water (2), Thames Water (1), United Utilities (1), Wessex Water (1), Yorkshire Water (1)
Formal acknowledgement of a set of actions (“Acknowledged Actions”)
10
Portsmouth Water (1), Severn Trent Water (6), Southern Water (1), South Staffordshire Water (1), South West Water (1)
Table 37 – PR24 Related Legal instruments issued in England, in 2024
Transformation Programmes
A key activity of the Inspectorate’s Enforcement Team is the management of the transformation programmes. The Inspectorate may initiate a transformation programme where the risk position of a company becomes elevated or is frequently realised in a specific area of operation. For example, multiple, similar drinking water quality events caused by a lack of appropriate training. Once a company is notified that we intend to place them into transformation, we seek to work collaboratively to put together a measurable programme of improvements.
A transformation programme includes a set of bespoke legal instruments to address those areas of high risk. They are generally large in scope and require a long-term, concentrated effort in order to move the risk position. Following the initial tranche of legal instruments, follow up legal instruments may be served to address issues that fall out of the initial programme.
Transformation isn’t only about completing the work under the notices, but it is about a robust and consistent effort to reduce overall risk. A large factor in this can be the attitude of company personnel, particularly those in senior leadership roles, who ultimately determine the attitude of the company.
There are currently four English water companies in transformation. A summary of the enforcement activities in 2024 and progress with transformation is given below.
Northumbrian Water
Northumbrian Water have been in Transformation since 2021, after a series of events and an increasing recommendation risk index score identified risks the company were carrying, particularly with respect to asset health.
Liaison meetings have been constructive in the main, with the company now highlighting issues earlier and they have noted that we are giving them more scrutiny than they had expected.
The management of the company’s Tanks and Service Reservoir notice has been poor. A total of five assets have been extracted out of the notice into their own individual notices, with another two currently still in draft. The lack of early planning for the difficult to isolate reservoirs and tanks does not give confidence that the notice, due to be completed by the end of March 2025, will be completed on time. One of the extracted tanks, the Gunnerton contact tank notice, was served in August 2024 but still requires dates for deliverables as a newly installed tank is required and the location is yet to be decided. This tank was only raised to the Inspectorate as an issue in the summer of 2024. The company had until the end of February 2025 to confirm delivery dates.
The company has been in transformation for three years, but have not mentioned the issues with this tank in meetings.. Most current notices are on track, but the failure of the Tanks and Service Reservoir notice has been a strong example of their poor management of legal instruments. The company is currently managing 32 legal instruments with five due for final reporting in 2025. Over the coming 12 months the company will be further scrutinised on their overall management of their legal instruments and their ambition to leave transformation.
Southern Water
Southern Water have been in Transformation since 2018. The company had begun an internal transformation programme, “Water First” prior to this, however the audits, compliance breaches and events which were still occurring required the formalisation into DWI specific transformation measures. Of the existing transformation companies, Southern Water have been in Transformation for the longest period.
New notices served during 2024 included a companywide discolouration notice, three water storage assets requiring enabling works for internal inspections, a companywide training and procedural notice aimed at network operations, and a replacement notice for the phased rebuilding of Weirwood works. Four regulation 28(4) notices were revoked in 2024, however that included the Yew Hill/West Hill notice, which was escalated to a Final Enforcement Order (FEO), Rownhams discoloration notice was replaced by the company-wide discolouration notice, the operational training notice was followed on by a network training notice and Weirwood saw a significant solution change that required a new notice. Thus, there were zero notices fully completed in the 2024 calendar year. A bulk supply metaldehyde section 19 undertaking was revoked.
Change applications submitted in 2024 resulted in one FEO, three new notices and five new versions of notices. Six change applications were rejected as the delays were deemed to have been caused by the company, or were fully within the company’s control. A list of these delayed schemes can be found below. Whilst the company does not have the most legal instruments in place, it by far applies for the most change applications. These applications almost always request to extend the dates of milestones and/or the final completion date within them. Since January 2020 an average of 1.5 change applications per month have been submitted, more than all other companies combined.
The company received its seventh FEO in August 2024. This was a result of failing to meet the requirements of the existing 28(4) notice covering Yew Hill SR and West Hill SR. These reservoir sites were unable to be removed from service for internal inspections or remedial works. Yew Hill SR had a crack along its side wall, with ingress which led to multiple failed microbiological failures since 2021. The notice had moved through a number of possible solutions, each of which pushed back the proposed inspection date. To ensure the inspection would not be delayed further, the latest change application was accepted as a FEO. The order was made on 14 August 2024, following consultation. A coliform detection from the reservoir was reported as an event in October 2024 highlighting the risk the reservoir poses to consumers in the Winchester area. The company have since fast tracked the isolation, inspection and remediation of the asset.
There have however been some green shoots starting to emerge. Following a strategic review, the Inspectorate undertook the serving of enforcement orders on the big four works (Otterbourne, Testwood, Hardham and Burham) and a new management structure was installed to provide more overarching responsibility for the sites and the multiple work streams that were required for complying with the orders. Since the enforcement orders have been in place, it has been a learning curve for the company as to what is expected in terms of evidence and reporting. In 2024 the reports submitted were vastly improved from 2023 and fewer queries and questions arose from them. Hardham and Burham works have seen a number of steps completed years ahead of the enforcement order dates.
Whilst the discolouration contacts made to the company cannot be viewed as good news, the company do appear to have pivoted from a reactive mindset to a new approach which is risk-based and outcome driven. If the solutions can remove the source of discolouration where possible, rather than simply flushing it through the system until it builds back up again, then the cause rather than the effect can be resolved.
Despite having been in Transformation for over six years, the company show few of the signs of overall improvement required to remove them from Transformation. They still suffer from large events occurring at sites covered by Legal Instruments. For example, four events occurred at Testwood in 2024. Audits still uncover a wide range of issues across the asset base and the company sit far above the expected average for their Recommendation Risk Index. The constant monthly submission of change applications outlines projects overrunning and delayed for a wide variety of reasons, mostly entirely within the control of the company. The Inspectorate will continue to apply pressure to the company until improvements are seen.
South West Water
South West Water have been in transformation since 2020 and received four transformation specific regulation 28(4) notices. These notices include Maintenance and Resilience Hazard Review, Service Reservoirs, Scientific Investigations and Cultural Change Programme.
The company has been in transformation for four years and are making positive progress with their current Legal Instruments. Regarding transformation notices, specifically the Cultural Change Programme, this concluded in January 2025 and Scientific Investigations by May 2025. The Maintenance and Resilience Hazard Review and the Service Reservoirs notices conclude in January 2027.
The company requested an extension to the existing Transformation Scientific Investigations notice. Three of the assets listed within the notice would require further works to gain access and this work would not be facilitated until further into AMP 8. The Inspectorate would not accept an extension, and three individual reactive regulation 28(4) notices were served on assets located within Dousland, Prewley and Lowermoor. A reactive section 19 SEMD undertaking was served on an asset within the Bristol region.
Transformation meetings have been constructive, and the water quality team proactively engage with Enforcement Inspectors. The company highlight issues early where possible.
South West water display a positive attitude toward the management of their legal instruments and have an ambition to leave transformation. The overall risk position of the company has decreased since the programme was initiated in 2020.
The Isles of Scilly still pose a significant water quality risk with three of the five schemes currently delayed; it is anticipated that the remaining two schemes will also become delayed. This issue is further compounded by the lack of an accredited regulation 31 laboratory to approve products in contact with drinking water, a risk the Inspectorate has talked about in these reports for many years now. The proposed solution to these five schemes depends upon regulation 31 approved products, which currently do not hold that approval. Putting an unapproved product into supply would constitute an offence under regulation 31 and therefore the company are proactively seeking a laboratory to undertake the testing requirements.
Thames Water
Thames Water entered the Transformation programme in 2018, following the identification of several deficiencies within the company’s risk assessment reports, and the realisation of these risks during site audits and the assessment of compliance and events. The transformation programme aimed to address several key areas of improvement where significant risks had been identified. The work areas included risk assessment and treatment of Cryptosporidium, management of turbidity, management of slow sand filters, training and competency of staff and risk from flooding. An initial tranche of 14 notices were served upon the company to address these risk areas, which have been followed by further notices to address other specific areas of concern. The company currently has 34 legal instruments in place, with a further three pending. Five notices are due for closure in 2025.
2024 has been a busy year for the company in terms of the management of its legal instruments. The company have submitted closure reports for several large transformation notices, which have now been assessed and revoked by the Inspectorate. The notices revoked include training and competency of staff, filter management and Cryptosporidium Hazard Review (HAZREV). In addition, the company submitted a closure report for the Data Shortfall FEO and several other notices, which have also been revoked by the Inspectorate. These are discussed in more detail in the highlights section below.
The company continue to engage with the Inspectorate, and quarterly transformation liaison meetings take place, alongside monthly catchup meetings with the Enforcement Team and the company’s Water Quality Team. The company have also invested in additional staff to improve reporting to the Inspectorate, which is seen as a welcome move and the improvement in the quality and timeliness of reports is already being realised.
The training and competency notice that was part of the initial tranche of transformation notices was successfully completed by the company in 2024 and revoked by the Inspectorate. The notice required the company to complete a critical review of competency, which found several shortcomings. Firstly, there was no standardised approach on recording competency, Secondly, the system for assessing competence was managed at a local level, resulting in varying levels of evidence. Thirdly, in terms of confidence of training, this was done via the company’s Performance Development Review Process. Fourthly, the company did not have a Licence to Operate scheme. This has now been introduced and aligned to the Industry Standard Competent Operator Scheme for all relevant business streams. The other issues identified have also been rectified. The audit strategy provided by the company for this notice showed an overall reduction in the numbers of events and failures when compared to previous years, prior to the issuing of the notice. It was also clear that the number of events and failures associated specifically with risks relating to training and competency had reduced since completing the notice. This is therefore a big achievement for the company and demonstrates tangible improvements companies can make when in Transformation.
The company also successfully closed the Cryptosporidium HAZREV notice, which was discussed in detail in the third quarterly report for 2024. It is noteworthy, however, to highlight that this notice covered 95 treatment works and was split into four sections, resulting in a complex notice to deliver. The notice remained the same version as when it was first served, without the need to be changed. Given its size and complexity, this demonstrates the company’s commitment to mitigating the risks that this notice covered.
Furthermore, the company submitted a closure report for the Data Shortfall FEO, which had been in place since January 2023, due to contraventions of regulations 6, 9, 12, 13, 14 and 17 of the Regulations. The Inspectorate assessed the information provided by the company and concluded that significant improvements had been made to the way the company approached regulatory sampling activities, including upgrades to technology and transport, additional training of staff and improvements in vehicles and resources. The Inspectorate entered consultation and subsequently revoked the FEO on 16 October 2024.
Finally, in addition to all the significant work outlined above, the company have successfully closed another five notices, demonstrating a high level of commitment to its Transformation programme.
Thames Water submitted two PR24 schemes for the Inspectorate to consider for support, for improvements in meeting the requirements of the Security and Emergency Measures Direction. The requested support was subsequently given. However, the company failed to submit section 19 undertakings to formalise the supported schemes. This was discussed in more detail in the third quarterly report from the Inspectorate, but is mentioned again here, as it represents a lowlight for the company, where the Inspectorate was left with no choice but to initiate further enforcement action. As a reminder to companies, the Inspectorate has no remit when it comes to financial matters, and will always seek compliance, using its published enforcement policies.
During an event assessment in the Guildford Water Supply Zone, deficiencies were noted in compliance with the Security and Emergency Measures Direction. The company were informed of the Inspectorate’s intention to initiate enforcement action but again declined to offer a signed section 19 undertaking. A second letter was sent by the Inspectorate, requesting a signed undertaking, and setting out that if an undertaking was not received, further enforcement in the form of an FEO would follow. The company subsequently offered a signed undertaking. Again, this serves as a reminder that the Inspectorate will always follow its published enforcement policies, to secure compliance.
Despite the positive messages regarding the original transformation programme notice progress, there have been other occasions where it has been a difficult, drawn-out process to secure legal instruments with the company. It is paramount that a company in transformation seeks to work with the Inspectorate to secure compliance. Ultimately, we are all trying to seek the same goal. Secure, wholesome drinking water supplies for consumers. The company have made real progress with their transformation programme, and its pleasing to see that measurable and substantial improvements have been made. The engagement from the company has been satisfactory, however, as discussed above, there have been issues with securing some legal instruments. The Inspectorate will always seek to work with companies to secure compliance, however, when companies undermine this process, the Inspectorate follow through and pursue further enforcement where necessary. Transformation programmes are not just about delivering a package of notices. They require real cultural change and quality dialogue at every level of the company to work with the Inspectorate to secure its success and exit the process. It is worth pointing out that the content of reports submitted to the Enforcement Team is very good, with minimal intervention required from the Inspectorate. The company should continue in this manner and work with the Inspectorate on initiation of its legal instruments in 2025 and beyond, to ultimately deliver significant improvements and risk reduction.
Delayed Legal Instruments
Delays to the delivery of projects can occur for all sorts of reasons. When notified of delays to programmes of work covered by our legal instruments, we consider they fall into two broad categories; those genuinely outside of the control of a company and those within the control of a company. Drinking water quality, security and emergency measures, or network and information systems improvement projects are important pieces of work, which should be taken seriously and delivered in a competent manner. The whole reason for their existence is the protection of wholesome drinking water supplies to consumers. Drinking water is a service that is essential for life and which must never be forgotten. We may be sympathetic regarding delays caused by matters that are genuinely outside of the company’s control and exceed a reasonable float of a project. However, we are less sympathetic to other delays and there are examples above where we have used our enforcement powers to ramp up the level of enforcement in response to unacceptable delays. The following table lists the legal instruments that were delayed as of the end of 2024.
Company
Legal instrument
Delays
Northumbrian Water
Linford works
Delays in land purchase
Northumbrian Water
Tanks and Service Reservoirs
Five tanks outstanding beyond notice date
South East Water
Tanks Inspection and Cleaning
30 tanks outstanding beyond notice date
South East Water
Tilford Meads Arsenic
Changes in solution and contractor issues
South West Water (Isles of Scilly)
Bryher Island Water Treatment Works Improvements
Delays in submitting planning application
South West Water (Isles of Scilly)
St Martins Island Water Treatment Works Improvements
Delays in submitting planning application
South West Water (Isles of Scilly)
Tresco Island Water Treatment Works Improvements
Delays in submitting planning application
Southern Water
AMP7 Mid Thanet Nitrate
Poor contractor management and governance
Southern Water
AMP7 Patcham Nitrate
Poor project management control and understanding of requirements
Southern Water
Burpham CWT Enabling Works
Poor contractor management
Southern Water
Dunkirk BPT Inspection
Completion report was rejected due to outstanding issues which now need to be addressed
Southern Water
Hardham / Laws Aquifer Combined and Cocking High Iron
Completion report was rejected due to outstanding issues which now need to be addressed
Southern Water
Service Reservoir Integrity
3 sites at risk of not meeting notice date
Table 38 – Delayed legal instruments at the end of 2024
Recommendations
The Inspectorate issued 836 recommendations in 2024, a significant increase on 714 in 2023 and 564 in 2022 . Recommendations are spread across the majority of companies with only some NAV companies not receiving any.
Company code
Number of recommendations
TMS
122
SVT
118
YKS
94
SRN
59
AFW
51
ANH
50
SEW
48
UUT
44
IWN
39
SST
35
NES
28
CAM
25
SES
24
SWB
18
BRL
17
WSX
16
ESP
14
PRT
11
ALB
7
LNW
6
ICW
5
ISC
3
VWP
2
Total
836
Table 39 – Number of recommendations given to each company in 2024
Regulatory breaches are the primary reason for making a recommendation where the company has failed to comply with the regulatory requirements which has resulted or could have resulted in a breach and a risk to wholesomeness. The Inspectorate made 112 recommendations where we felt that there was a serious breach of regulation.
A breach of regulation 27 (risk assessment) was the most common failing with 264 recommendations made, associated with shortcomings which the Inspectorate considers would have been within the company’s control and should have been proactively managed. Failings associated with disinfection and treatment resulted in 157 recommendations whilst failings associated with materials in contact with drinking water (Reg31) resulted in 30 recommendations. No one company stands out on Reg31 issues with regards to recommendations however events related to Reg31 are covered in the specific section.
Regulations breached/likely to have breached
Number of regulatory breaches
Risk assessment (Reg 27, 28 in W)
264
Wholesomeness (Reg 4 in E&W)
232
Investigations (Regs 18 and 19 in E&W)
175
Disinfection and treatment (Reg 26, 27 in W)
157
Sampling and analysis (Reg 16 in E&W)
64
Notification (Reg 35(4); 35(6) in W)
35
Materials and products (Reg 31 in E&W)
30
Monitoring (Reg 6 in E&W, also 13,14)
12
Additional monitoring (Reg10 in E&W)
7
Number of samples (Reg 9 in E&W)
3
Water industry act
3
Information direction
1
Sampling points (Reg7 in E&W)
1
Total
836
Table 40 – Number of recommendations given by regulatory breach
Lead in water
Lead is a toxic metal that can dissolve into the drinking water supply when water comes into contact with lead pipes. The source of lead in drinking water is mainly communication pipes owned by water companies and supply pipes owned by consumers within their property which are made from lead. There were 53 compliance sample failures for lead during 2024 out of 13,394 samples analysed for lead. Consumers are, to a large extent, protected from exposure to lead by the practice of phosphate dosing at water treatment works to reduce plumbosolvency. To further reduce exposure to consumers from lead, anational and company strategy is required to mitigate the risk.
Lead contributed to 54 events reported to the Inspectorate in 2024.The combined ERI score for these events was 2.337. The majority of the ERI score was attributable to a single event which affected 512 consumers in a school where one communication pipe and one supply pipe were identified to be lead along with presence of lead solder. In this instance the company undertook the correct action and issued a section 75 notice to the school requiring the school to investigate, identify and replace any sources of lead.
The Inspectorate collects data on lead via the compliance process which sets out how many compliance samples must be taken each year from water quality zones, this number varies by population but as a maximum this is 8 samples per year per zone as stipulated within the water quality regulations. Therefore, the size of the data set held for lead is quite small compared to the amount of data held on other parameters. Companies, however, do collect far more data than the compliance samples we require them to take. The Inspectorate has been in discussions with the industry lead working group to see whether all lead sample data can be collated on behalf of the industry to help the Inspectorate and form an overall picture of the lead risk within the country. Holding this data set would enable the Inspectorate to work better with Defra and central government to be able to advocate for changes to the governmental policy for lead management within water.
Lead is a problem which to a large extent is confined to within the boundaries of homes and therefore is under the control of the homeowners to rectify, it is however a relatively invisible problem and one which is tough to compel homeowners to spend the often large amount of money required to remove lead from their properties. Large-scale company-led removal schemes have been successful in discrete areas, but scaling up to national levels is not currently feasible.
The issue is also compounded by the fact that some plumbers still use lead solder despite it being banned for use on cold water systems. Using this lead solder on hot water systems is still possible and lead solder can still be purchased from plumbing and DIY shops should the homeowner be willing to carry out their own modifications which, unlike the gas industry, is still legal to do so. There is an approved plumber scheme in place, but there is no legal requirement to use this service.
The World Health Organisation (WHO) has declared there is no safe level of lead in drinking water. Many lead pipes still exist within company distribution networks, particularly on the final sections of pipe supplying consumer properties. The Inspectorate set out its expectations in respect of lead in its long-term planning guidance. Water companies have collectively declared an ambition to be lead pipe free by 2050.
Materials in contact with drinking water (Regulation 31)
Regulation 31 prohibits a water company from applying any substance or product to, or introduce any substance or product into, water which may impact drinking water quality. This covers all chemicals, construction and treatment products used by water undertakers, from the source of the water, up to the point of delivery to the consumer’s building. This is a critical duty because materials can taint water by taste, odour or by leaching of harmful substances. The regulation sets out how approvals can be given to construction and treatment products and materials that do not prejudice water quality and ultimately consumer safety.
During 2024, the Inspectorate continued to receive and process applications for approval of products in contact with drinking water (under regulation 31). The volume of applications received was:
Year
Total applications
New applications
Product changes
Product reapprovals
2024
177
47
79
51
2023
126
24
61
42
2022
145
32
62
51
2021
146
23
62
60
Table 42 – Regulation 31 applications, changes and reapprovals
The Inspectorate has continued working with its IT partners to further develop the regulation 31 portal for product approvals. The system has replaced the previously used manual application forms with online, interactive application forms that will guide applicants in providing all the necessary information for an approval or product change to be considered. The online process will have the benefit of meeting accessibility standards, making them available to more people with the next phase of the project delivering and end to end process and approved products list transformed from a monthly, published PDF document to an interactive, searchable website which is updated in real-time. This will effectively become a live, online catalogue of approved products.
A significant increase in poor product stewardship was seen in 2024 with approved products being revoked from the Secretary of States List with immediate effect and a notification letter of prohibition issued for the use of a product with an unauthorised name change. Subsequent investigations led to further revocations in early 2025. All issues identified were as a result of unauthorised changes being made.
In December 2024 a revocation was applied to Puriton Pipes (DWI 56/4/1112) manufactured by Radius Systems Ltd. The company had made a late submission for the reapproval and once all the relevant documents were submitted, the reapproval was granted. Subsequently however, the Inspectorate was informed that the information provided was incorrect and that unauthorised changes had been made to the product. This resulted in the immediate revocation of the product and extensive liaison with the company. The water industry was informed of the revocation via a regulation 31 information letter (ref: R31-03/2024)
A Notification Letter (ref R31-01/2024) was issued to the industry following an unauthorised name change to an approved product which prohibited its use. As part of a rebranding process, MBCC provided suppliers with products labelled with a handwritten label stating the new Sika product name, Sikadur-CombiFlex 930 with Sikadur-CombiFlex 933 (DWI 56/4/1569), and this was accompanied by the MBCC IFU document for MasterSeal 930 joint bandage with MasterSeal 933 adhesive (DWI 56/4/144). The product name and the details on the IFU should be identical. This was initially identified by Northumbrian Water who notified the regulation 31 team. This was subsequently found to be a widespread issue.
The company had not completed the change process for this product which resulted in several companies having to remove the product from assets where it had been applied, with other companies forced to keep assets out of supply until the process had been completed and the name change authorised. This resulted in a significant number of meetings with water company representatives and the manufacturer to rectify the issue during what was an already busy period for the team.
This was yet another example of both poor product stewardship by the manufacturers and complacency on behalf of water companies and contractors who failed to identify that the IFU did not match the label on the product container, and the product name did not appear on the List of Approved Products. As a result, water companies were requested to notify use of this product to the Inspectorate as an event.
The Inspectorate does not take the decision to revoke products or prohibit the use of products lightly, however, where the stringent requirements to maintain the product approvals are not met, and constitutes a potential concern to public health, this threshold is met.
In addition, a large number of approval holders either made late applications or omitted to apply for product reapprovals which resulted in a delay in reapprovals being assessed and an increase in expired products with manufacturers having to undertake the entire process of product approval from the beginning.
These incidents were extremely time consuming for the small regulation 31 team to manage and impacted the growing back log of applications. A decision was taken to prioritise reapprovals during this time to ensure continuity of product availability.
The team were also involved in the development of the new Materials in Contact awareness course being offered by EUSR and continue to work on various EN standards covering treatment chemicals, filter media and material leaching, biocides and radioactivity along with managing some research projects. We continue to receive large numbers of enquiries relating to Water Fittings regulations such as recirculating showers, grey water reuse and wider recycling schemes.
There has been significant work undertaken by the team to secure testing facilities for BS6920 and full regulation 31 testing throughout the year. We are also collaborating with the water industry to resolve the issue, and this work is ongoing. Laboratories are required to demonstrate and evidence compliance with the relevant standards to become designated for regulation 31 testing.
Anglian Water – Regulation 31 Case
At Northampton Magistrates court on15 May 2025, Anglian Water was fined a record £1.42 million following a prosecution by the Drinking Water Inspectorate for drinking water failures affecting around 1.3 million people.
Between June and December 2021, Anglian Water notified the Inspectorate of four water quality events where unapproved pipework and material was used in several tanks in the supply of drinking water.
Anglian Water pleaded guilty to five offences under regulation 33 by virtue of failure to comply with regulation 31(1) of the Water Supply (Water Quality) Regulations 2016 (as amended) for repeatedly introducing non-compliant materials into the water supply. The investigation identified compelling and credible evidence for the following failures and findings at four separate sites.
Issues common to each event
The investigation identified compelling and credible evidence for the failures and findings below (common to all 4 schemes):
Lack of control of the regulation 31 process to prevent the installation of unapproved products in a submerged environment repeatedly (strong evidence pointing to failure to control products used, backed with witness statements, contractor witness statements, photographs and Materials in Contact records)
Poor management of contractorsand supply chain/procurement arrangements (backed by witness statements, procurement and delivery records)
Lack of regulation 31 training in place at the time of installation for engineers, water quality, or project managers (training records, witness statements)
The coating of the pipes (in all events) deteriorated to a powder/flakes that was easily removed from the surface of the pipes. The analysis of the coatings contained controlled phthalate-based substances, some of which are banned from children’s toys, cause birth defects and cancers (evidence includes compound analysis reports, SNARLS, pictures, and witness statements).
Water quality monitoring did not detect a deterioration in quality (except at Kedington works (see below), – however not all relevant parameters were analysed regularly and consistently (evidence included sampling records).
At Kedington works, Anglian Water detected a taste described as “sweet” by two laboratory analysts, from a sample of the unblended treated water on 11 May 2020. This is an unusual taste for drinking water and could have been as a result of paint particles, subsequently shown to contain xylene, impacting on the quality of the water being supplied.
Approximately 1.3 million customers across the Anglian Water region have been impacted by these failures. The Inspectorate was critical of the wrong products being used in submerged environments, lack of controls and of the company’s management of products. The Inspectorate was also critical that an asset remained in service after it had been identified that non-approved products were being used.
Failure to control the installation of unknown and untested materials can have consequences; this prosecution serves as a reminder that drinking water must come first as a service.
Security and Emergencies (SEMD)
2024 was the third reporting year for companies since the Inspectorate has regulated the Security and Emergency Measures Direction. Companies have demonstrated an overall improvement in recognising the areas that they need to improve and move towards compliance with the Direction, resulting in significant investment in PR24 over a range of schemes consisting of security and emergency planning improvements.
During 2024, the Inspectorate observed increased engagement from the Industry looking to proactively enhance compliance with the Direction, for example the Inspectorate hosted an emergency planning specialist from a water company who was seconded to the Inspectorate for a six-month period, under our better regulation programme. This enabled the company to gain first hand knowledge and regulatory understanding of the DWI’s expectations of water companies’ compliance with SEMD as well as the Inspectorate gaining an insight into the practicalities experienced by water companies of planning and running emergency incidents.
The Inspectorate undertook a program of audits as well as event assessment and company interaction which resulted in a range of enforcement activity to secure improvement and compliance as demonstrated below.
Figure 37 Table 42 – SEMD enforcement overview
Audits completed
25
Enforcement orders made
2
Undertakings served
4
Recommendations made
86
The industry has fed back that this enforcement led approach is a step change from the previous SEMD regime prior to DWI’s involvement.
Water companies have made notable progress in complying with SEMD requirements, with evidence of improved outcomes and compliance emerging, with more to deliver in AMP8.
SEMD Audits
During 2024, the Inspectorate undertook 25 SEMD audits of water companies across the industry. The purpose of the audits was to review companies’ security measures at water sites including an analysis of procedures and physical site security measures, an industry wide testing and exercising audit looking at companies exercising programs and emergency response as well as a command-and-control audit of a water companies emergency planning function. The findings and recommendations resulting from these audits were formally shared with security and emergency planning managers from the relevant companies. In several cases, enforcement was required for non-compliance with the Direction, ranging from the service of Section 19 Undertakings to Final Enforcement Order.
RAG (Red/Amber/Green) submission
2024 was the third year for the risk assessment RAG returns, as companies continued to work to benchmark against the expectations of SEMD 2022(as amended) and the rest of the industry.
Overview of RAG Movements
Since 2022, the companies red and amber self-classifications have increased, as expected in the initial years of assessment following feedback of events and audits and peer to peer benchmarking:
Figure 38 – Changes in RAG assessments 2022 – 2024
The most significant shifts in RAG status typically follow an audit or major event.
In contrast to previous years, the greatest movement in 2024 was observed in the Testing and Exercising category, coinciding with industry wide audits being submitted alongside RAG assessments.
Inset Appointees are not represented in the datasets, as they follow a different reporting mechanism.
Notable RAG outcomes include:
Vulnerable Customers
Similar to last year, many companies reported Amber and Red for vulnerable customers. Several companies cited problems with linking existing Priority Service Register (PSR) customer data with customer systems as well as highlighting issues of data sharing agreements and varying support from external agencies, such as Local Resilience Forum (LRF) partners, providing uncertainty about the ability to meet the demand for vulnerable customer deliveries.
Several companies have developed systems to improve liaison with vulnerable consumers. South East Water introduced a new SMS text messaging system of informing vulnerable customers of water disruptions. Companies reporting Green had detailed information on vulnerable sites in their remit for example using tactical mapping processes to identify vulnerable customers, hospitals, schools, nursing/care homes and prisons. Several companies had hospital and prison plans in place which containing key information to increase understanding and support of these customers during any incidents.
Testing and Exercising
The 2024 RAG submission coincided with an industry wide audit of testing and exercising, and the 2024 submission saw numerous companies move to amber in their RAG status for these outcomes. Several companies reporting amber had not exercised their reasonable worst case scenario in terms of alternative water provision. We saw one company recognising this and they are now looking to exercise their biggest island zone. Other companies noted a lack of testing of vulnerable sites such as prisons and hospitals.
Some companies listed a number of “live incidents” as testing and exercising but didn’t identify which objectives were met which were still outstanding with limited post incident reviews to maximise the learning. Some companies have implemented a post incident review process to capture learning after each incident and exercise, which is supported by centralised action trackers to monitor progress of actions and a governance framework in place to escalate overdue actions, this was welcomed by the Inspectorate. Most companies carried out testing and exercising with Local Resilience Forum (LRF) partners, however other companies just took part in LRF organised exercises and took limited learning from these, whilst others proactively organised and engaged with the LRF in water related incident scenarios, this was also welcomed by the Inspectorate.
Those companies reporting Green for the testing and exercising outcome typically undertook live emergency planning testing with external stakeholders as well as several companies testing a variety of alternative water deployment, from setting up alternative water stations, deployment of static tanks and tankering exercises. These exercises had clear aims and objectives with documented learning embedded in the company. In addition, several companies reporting green had undertaken a variety of security testing including penetration testing of sites and assets, bug sweeps, email phishing tests, as well as the placement of dummy signs at a site to test security reporting exercises.
Identification of external suppliers
Companies reporting green used tools such as risk ledger where businesses with heightened security risks are signed up to the platform providing an assessment of the security risks posed by these organisations. In addition, other companies mandated that their supply chain are required to complete criminal declarations and identification checks before work on operational assets with access to sites being a controlled process requiring sign off. One company implemented personnel security checks for temporary employees delivered to the same standard as those conducted on employees.
Events and Incidents
Social media auditors have presented a challenge for several companies during 2024, and whilst they are normally legal, this has highlighted a number of issues for the companies involved. We did however see a few examples of positive behaviours around challenging and engaging with the social media auditors.
Over the year we also spoke to several companies regarding revealing too much information about sensitive sites, this can be from site tours which are specifically prohibited, to industry write ups on large construction projects. The Inspectorate reminded and continues to remind companies of their obligations to keep critical information secure.
Notable events include:
Southern Water – Hasting loss of supply
Between 2 May 2024 and 7 May 2024, consumers supplied from a treatment works in Hastings lost drinking water supplies due to a burst on the incoming raw water main supplying the treatment works. This was notified to the Inspectorate as drinking water quality event 2024/9637. During the event, the company failed to comply with the requirements of paragraphs 3 and 4(4) of the Direction.
The company had previously acknowledged that the main required replacing, but this was not done due to cost, it was noted on the company risk water safety plan as a category D requiring further mitigation as well as being the cause of previous loss of supply and burst event. Therefore, the Inspectorate concluded that the company did not have in place adequate resilience plans to ensure the continuance of all its water supply functions, which is a breach of paragraph 4(4)(a) of the Direction, which states that plans for water supply must be prepared on the basis that the company must (a) continue to carry out (i) all of its water supply functions.
Therefore, following the event, the Inspectorate enforced, and the company have offered a Section 19 Undertaking to replace the main and improve resilience to the area.
Affinity Water-YouTube Incident
The event concerned YouTube content creators gaining unauthorised entry and filming water company tunnels at a reservoir and borehole site, bypassing security measures and entering through an insufficiently secured door. The resulting video, uploaded in January 2024, prompted the company to investigate and report the incident to the Inspectorate. The security breach was attributed to a faulty lock, and the company acknowledged delays in alarm response. Remedial actions included securing the door with additional locks, installing a secondary security detector, and implementing regular maintenance checks as a short-term measure. The door was subsequently replaced with measures put in place to address the alarm response.
The Inspectorate recommended a comprehensive review of the company’s security maintenance strategy and communication protocols. The Inspectorate emphasised the need for timely alarm responses and thorough checks of all access points. The company was required to submit a detailed review of site security, confirm the security rating of new door fittings, and ensure that future breaches are detected and addressed promptly.
Thames Water – Guildford loss of supply
Following an extreme weather incident at the end of 2023 (Storm Ciaran), the company experienced outages at eight pumping and treatment sites across the Guildford supply system and a subsequent widespread loss of supply was experienced across the Guildford area. This was due to the number and duration of outages at Shalford treatment works during this period, as well as the lack of water/power supply resilience within the Guildford system.
Following the Inspectorate’s assessment of the event, we wrote to the company with a minded to enforce letter requesting a Section 19 Undertaking to be signed by the company to deliver improvements to emergency planning and power resilience within the Guildford area. The company accepted the Section 19 Undertaking in November 2024 which requires the company to carry out action to improve resilience in the Guildford area.
Southern Water- Testwood loss of supply
A significant water quality event at Testwood water treatment works occurred on December 18, 2024, involving plant failure and loss of supply. The event led to elevated turbidity levels and subsequent shutdowns, causing a loss of supply for 130,920 consumers. The company took various actions, including forming an incident team, setting up bottled water stations, and rezoning their network to bring in water from other areas. The company stated they faced challenges in setting up bottled water stations and ensuring timely deliveries, impacting their ability to provide the required minimum water supply to affected consumers.
The Inspectorate in their investigation highlighted the need for better planning and execution of alternative water provisions during emergencies and recommending reviewing the company’s methodology for assessing bottled water station locations and improving the resilience of alternative water supplies, particularly for vulnerable sites like hospitals. Additionally, we highlighted the need to review network storage and response capabilities to handle similar incidents more effectively in the future. A ‘minded to enforce’ letter, requesting a Section 19 Undertaking was sent as part of the event write up, requiring the company to undertake works to increase resilience at the site.
Southern Water – Secure minded communications
In January 2024 we wrote to Southern Water regarding an online article that showed detailed valve drawings of a CNI site. There were several concerns with this article such as it revealed locations of sensitive assets and listed names of the key supply chain used to deliver this project.
We formally recommended the company ensure that future publications do not reveal sensitive information within the article, and we suggested that the company removed this existing article from the website. The Company responded by removing the article, stating no further articles relating to CNI sites will be published and relevant processes and procedures reviewed around publication of information
Audits undertaken by the SEMD team in 2024
Company
Audit area
Audit theme
Date of audit
TMS
Physical
Security
Jan-24
TMS
Physical
Security
Jan-24
TMS
Physical
Security
Jan-24
AFW
Physical
Security
Jan-24
SRN
Physical
Security
Feb-24
AFW
Desktop
Testing and Exercising
Apr-24
ANH
Desktop
Testing and Exercising
Apr-24
DWR
Desktop
Testing and Exercising
Apr-24
HDC
Desktop
Testing and Exercising
Apr-24
NES
Desktop
Testing and Exercising
Apr-24
PRT
Desktop
Testing and Exercising
Apr-24
SES
Desktop
Testing and Exercising
Apr-24
SEW
Desktop
Testing and Exercising
Apr-24
SRN
Desktop
Testing and Exercising
Apr-24
SST
Desktop
Testing and Exercising
Apr-24
SVT
Desktop
Testing and Exercising
Apr-24
SWB
Desktop
Testing and Exercising
Apr-24
TMS
Desktop
Testing and Exercising
Apr-24
UUT
Desktop
Testing and Exercising
Apr-24
WSX
Desktop
Testing and Exercising
Apr-24
YKS
Desktop
Testing and Exercising
Apr-24
BRL
Physical
Security
May-24
SES
Physical
Command & Control
Jul-24
HDC
Physical
Security
Oct-24
YKS
Physical
Security
Nov-2
Table 43 – SEMD audits in 2024
24 Audits were undertaken in total with 3 carried out in Wales.
Network Information systems (NIS)
The Network and Information Systems Regulations (2018) is a regulation to ensure the operational technology which maintains the production of drinking water remains robust and operational, to ensure water is delivered at all times. In England, the implementation and operational delivery of the NIS Regulations is delegated to the Drinking Water Inspectorate. The strategic purpose is to ensure that water companies deliver the essential service of providing uninterrupted, wholesome water supplies to consumers in England.
Operational Technology (OT) refers to the hardware and software systems used to monitor and control physical devices, processes, and infrastructure in industrial operations. It differs from Information Technology (IT) by focusing on the physical world and its control rather than data processing and management. Such technology controls the operation and automation of equipment used for the abstraction, treatment and distribution of drinking water (e.g. forwarding pumps, chemical dosing pumps, valves, water quality protection shut-down systems, as well as automated safety systems). OT is a critical component for the automated, safe, cost-efficient production of wholesome drinking water. To protect the essential service, the technologies employed need to be suitable, secure, and fit for purpose to ensure continuous reliable production and to simultaneously defend against continually evolving threats to our critical national infrastructure
Examples of OT include industrial control systems (ICS) such as Supervisory Control and Data Acquisition (SCADA) systems for drinking water treatment and distribution. SCADA is a system of software and hardware components that allow the automated operation of industrial processes locally or at remote locations. It is used to monitor, gather, and process real-time data; directly interact with devices such as sensors, valves, pumps, and motors. Other examples of OT include Human Machine Interfaces (HMI) which are screens, or interfaces that connect humans to a machine, system, or device. Programmable Logic Controllers (PLCs) are small industrial computers, with various inputs and outputs, used to control and monitor industrial equipment based on custom programming. Access to such technology by threat actors with disruptive intent would have potentially serious consequences.
Figure 40 – SCADA system (AI image)
Water companies serving a population of 200,000 people or more must implement a risk assessment to improve the resilience of OT. The sector uses the NCSC Cyber Assessment Framework (CAF) at the request of the DWI. Since 2018, the Inspectorate has received a CAF return annually from each company falling within the NIS regulations.
The companies map their resilience to threat actor capability against 39 contributing outcomes of good cyber practice. This risk assessment informs investments plans and areas requiring additional controls.
Figure 41 – password on instrumentation (AI image)
Between 2023-2024 every water company has been subject to a DWI cyber resilience audit to verify each company’s self-assessed CAF assessment. Two companies were issued with legal notices to improve their risk assessments in response to the audits. Every company in England (and Wales) has a regulation 18 notice to address residual cyber risk and their PR24 cyber improvement plans. Ofwat Price Control Deliverables are tied to these notices being met in full. Failure to meet the notice requirements may attract Ofwat penalties in addition to any DWI enforcement.
Research publications
The following research projects have been published throughout 2024.
This report comprises of the outputs of a study conducted on behalf of Defra and the Drinking Water Inspectorate to gather current knowledge on dual pipe water recycling systems at both national and international levels. The aim of this research is to review the current risks from such systems and the suitability of English and Welsh regulation to manage these risks and evolving systems.
The research project found that many large scale dual pipe systems in the UK have either been mothballed or have never become operational. The reasons for this are unclear, but international experience suggests cost, maintenance, and inconsistent public support for recycling are factors.
The research suggests some actions for further evaluation, to reduce the risks and enable the safe expansion of dual pipe systems and water recycling schemes, including:-
Separate regulations for dual supplies and drinking water regulations, to provide a coherent governance framework for recycling schemes.
Comprehensive types of dual pipe schemes (in terms of both source water and end uses)
Targets for water quality based on the source water and the intended use.
A single source of updated guidance for scheme designers, installers, and operators.
The research project has highlighted opportunities to resolve guidance differences between regulators and legislators. Water quality legislation does not currently distinguish between water for bathing or consumption and water for other domestic purposes (such as toilet flushing). Currently, all water used for domestic purposes must be wholesome (i.e. of a drinking water standard) as per the relevant water quality legislation.
The Drinking Water Inspectorate commissioned research on the regulatory framework and regulation of private water supplies (PWS) to understand its impact and how this framework could be improved to safeguard consumers of PWS. This research was undertaken by WRc, and they have produced separate reports for England and Wales.
Although public and private water supplies are subject to the same water quality standards, the risk assessment and monitoring of PWS and resulting enforcement is less rigorous. Current water quality legislation does not safeguard the health of all consumers equitably. A significant legislative gap means that single dwellings with a PWS, which constitute a significant proportion of the total, are not subject to regular risk assessment and monitoring. The number of water quality tests which fail the standard for total coliforms and E. coli is around one hundred times greater from private sources than from the public water supply.
While there has been an improvement in compliance with standards since 2010, most likely due to regulatory activities being focused on prioritised regulation 9 supplies (large, plus any used for commercial or public activity) progress from 2020 onwards has stalled. Due to the variability, inconsistency, and an inadequate mechanism for collecting and collating PWS water quality data, it is not possible to demonstrate an evidential link between the introduction of risk assessment activities and its impact on water quality.
There are economic barriers to connecting PWS to public water supplies where it is feasible, resulting in public supply connections being a non-viable option, even when a PWS poses a risk to health.
Local authorities are the regulators of private water supplies, but the availability and funding of sufficient experienced practitioners in local authorities (LAs) results in the regulations not always being enforced, water quality sampling sometimes being inadequate and mandatory risk assessments not always being in place. None of the LAs interviewed as part of the research, commented that they routinely enforce based upon risk assessment alone in the absence of failed test results.
Progress is recommended in areas including legislative harmonisation, a review of risk assessment and sampling practices, and the provision of additional powers to regulate and audit. The evidence from the review and stakeholder engagement suggests that a revised regulatory framework would deliver significant benefits in the medium term, without the need for centralised regulation. To resolve the uneven application of the legislation by LAs, training and toolkits should be provided, and the sharing of good practice and collaboration should be facilitated.
The report made a number of recommendations for areas including the creation of an overseeing body with the powers to enforce and audit. The relevant legislation should be harmonised and modernised, additional resources should be found for Local Authority Private Water Supply teams and additional independent research should be commissioned.
This project aimed to determine the scientific relevance of any prescribed standard for Microcystin-LR (MC-LR), its occurrence in raw surface waters, treated water concentrations, risks to consumers, and the suitability of analysis methods for cyanotoxin monitoring.
Cyanobacteria produce a wide range of cyanotoxins that are potentially hazardous to health. A health Guideline Value (GV) of 1.0 µg/L of total (intra + extra cellular) microcystin-LR in drinking water has been proposed by the World Health Organisation (WHO) and has been adopted by the Scottish government. However, this compound only needs monitoring “in the event of a potential bloom”.
The need to understand the occurrence of cyanotoxins and their potential risk is exacerbated by the increasing frequency of bloom occurrence as a result of climate change and accelerated rates of eutrophication due to human activities such as farming and (treated) wastewater effluent. Consequently, there are a wide range of policies that could have an impact on cyanotoxin occurrence.
A survey of water companies found that whilst cyanobacteria were commonly detected in UK drinking water sources, microcystins (the only cyanotoxin monitored) were infrequently detected and at low concentrations. A review of current literature also demonstrated that there is no universal definition for an algal bloom, which undermines any proposed requirement that microcystin-LR (MC-LR) only needs monitoring in the event of a potential algal bloom.
A single analytical method was developed for the detection of MC-LR, MC-RR, MC-YR, MC-LA, cylindrospermopsin, anatoxin-a (nodularin) by reverse phased LC-MS (liquid chromatography-mass spectrometry). A separate method using HILIC (hydrophilic interaction liquid chromatography) LC-MS was developed for the detection of saxitoxin.
Cyanotoxins were monitored throughout 2023 in raw and final waters at five sites in England and Scotland. Microcystins were detected in raw water at two out of the five sites and concentrations were mostly <1.0 µg/L (< 0.2 µg/L outside of the summer months and generally < 0.5 µg/L during the ‘peak’ season).
No cyanotoxins were detected in the final waters indicating that the risk to consumers is low.
It is recognised that the data generated in this study is only representative of one year. Risk from cyanotoxins should remain under review given that the frequency of algal blooms are expected to increase with climate change.
The main aim of this work was to enhance risk-based preventative strategies for maintaining drinking water safety by providing precise data on the prevalence and elimination of enteric pathogenic viruses at Drinking Water Treatment Plants in the UK. Given the current data deficiency regarding virus prevalence in UK drinking water sources, this research offers a novel perspective through appraisal of UK drinking water sources providing baseline measurement of somatic coliphage levels.
This research accomplished two key objectives:
optimized procedures for viral concentration and extraction from both surface and groundwater sources.
quantified the presence of somatic coliphages across 13 different drinking water sources, documenting their removal at different treatment stages based on 96 sample analyses.
Notably, no somatic coliphages were detected in the final treated drinking water samples, validating the efficacy of most current drinking Water Treatment Plants procedures in adhering to the EU’s requirement of nil plaque forming units (PFU)/100 ml. The study provides insights into drinking water sources with the identification of sources of historical risk for human enteric viruses (when somatic coliphages exceed 50 PFU/100ml), indicating the necessity for proof of viral log reductions across the treatment process. Future integration of this study’s catchment-specific data into a hybrid quantitative microbial risk assessment model could greatly assist in evaluating drinking Water Treatment Plants operation, ultimately contributing to the reduction of exposure to viral risk and regulatory non-compliance
Raw water data
Treated water regulation has long mandated efforts to ensure the safety of our drinking water. This is the overarching purpose of the Inspectorate, which has been analysing and reporting the quality of water around England and Wales since 1990. The regulations define safe ranges of chemicals in the water, and enforces action where companies fail to meet these requirements post-treatment. In 2024, this ranks the UK as joint first country in the world for drinking water quality, with an EPI Score of 100.0 for sanitation and drinking water. However, there is no official regulation on safe levels of pre-treatment raw water.
In the past century, water quality stressors have been primarily anthropogenic, with increasing freshwater demand and the polluting consequences of the urban, industrial and agriculture sectors. With climate change driving the increase in frequency and severity of extreme events such as storms and floods, inland water quality is set to continue worsening beyond these human factors. This will further strain treatment works and threaten drinking water supplies, and thus, there is a need for a more comprehensive quantification of raw water quality, to understand past and current trends through data.
In 2024, the Inspectorate commissioned a research project in association with the University of Cambridge to analyse the raw water dataset currently held by the Inspectorate to see what insights could be generated. The dataset currently comprises of:
~22.1 million total samples;
~13.5 million are groundwater
~8.4 million are surface water
764 parameters;
3,258 sites.
Figure 42 – Sampling locations – some data outliers can be seen and the DWI is investigating these errors
The project aims to deliver a tool which can be initially used for prediction of a small set of parameters to enable effective analysis with the potential to expand the number of parameters at a later stage.
A better understanding of the evolving distributions of different chemicals across the country will facilitate data-driven prediction of contamination risks and potential for polluted drinking water. Understanding how these propagate through treatment works could enable the prevention of these events, enabling water suppliers to handle transient increases in chemical levels in raw water. The DWI has been collating monthly raw water quality data collected by water companies since 2009, but has thus far been mostly focusing on monitoring and analysing compliance data from treated water. Analysis of this raw water dataset will support the Inspectorate in assessing the action, or lack thereof, of water suppliers in these cases. It will also help identify hotspots and highly stressed areas that might begin to struggle to provide drinking water up to regulatory standards in future.
The project continues into 2025 with the aim to complete the interactive tool focusing on the initial small number of parameters selected, with ideas around future work to expand this analysis to cover a more extensive range.
Whistleblowers
The Chief Inspector of Drinking Water and Inspectors appointed under section 86(1) of the Water Industry Act 1991 became ‘prescribed persons’ and are part of the Prescribed Persons Order 2014 as amended (the Order). This means that any employees, ex-employees, or contractors can report information to the Inspectorate concerning wrongdoing (known as whistleblowing) and will be afforded certain protections under the Order and the Employment Rights Act 1996. In general terms, a person passing on information concerning wrongdoing (making a disclosure) should not suffer detriment or victimisation from their employers.
The type of disclosure that would typically qualify as a protected disclosure under the Order would be if it relates to the quality and sufficiency of water supplied by the water industry, and the security of network and information systems within the supply and distribution sector. This will likely be information pertaining to a breach or potential breach of the Water Supply (Water Quality) Regulations 2016 (as amended), the Security and Emergency Measures Direction 2022 as amended (SEMD) and the Network and Information Systems Regulations 2018 or the company not meeting its obligations relating to water quality or sufficiency or potentially committing an offence under the Water Industry Act 1991.
Any persons wishing to report a concern or potential concern regarding suspected or known wrongdoing which the Inspectorate can investigate should do so by contacting the DWI Enquiries line (dwi.enquiries@defra.gov.uk or 0330 041 6501). The Inspectorate treats all disclosures made by whistleblowers sensitively and seriously and follows up each disclosure with an appropriate investigation. The Inspectorate will protect the identity of any individual making an allegation wherever possible. However, in certain circumstances the Inspectorate may be required to reveal the identity, if required by law.
Eleven disclosures have been made to Inspectorate for the reporting period 1 April 2024 – 31 March 2025. Of the eleven disclosures made seven required further investigation. One disclosure was referred to an alternative body. Relevant action was taken from five of the disclosures made after these were investigated by the Inspectorate. This included the issuing of recommendations and legal instruments.
The Inspectorate encourages water companies to have processes in place for employees and contractors to be encouraged and feel that they can speak up to report concerns around working practices which may impact on the company’s duties to meet its regulatory and statutory obligations for drinking water quality and network and information systems.
To help foster an open and supportive culture the Inspectorate encourages companies to take initiatives such as a reporting line for water quality and network information system concerns (similar to which some companies have in place to report health and safety concerns) and to have a formal whistleblowing policy in place, which is also encouraged by the Department for Business, Energy & Industrial Strategy who has published a whistleblowing guidance for employer’s code of practice.
Working with stakeholders
The Inspectorate works with a wide range of external organisations, other regulators, government departments, professional bodies and academic institutions in the delivery of its strategic objectives
Figure 43 & table 44 – Current DWI stakeholders
Current list of stakeholders includes, but is not limited to, the following:
Water suppliers
Other Regulators
Legislators
Research
Health Protection
local government
consumers
water practitioner groups
national cyber security centre
OFWAT economic regulator
Environment Agency
natural resources Wales
English and Welsh government
research universities
UK water industry research
UK health Security Agency
centre for communicable disease
local authorities for private water supplies
vulnerable customers
consumer council for water
water companies wholesale and retail
water UK
supply chain and contractors
laboratories and analytical services
British Geological Survey
water resource planning groups
health and safety executive
natural England
Food Standards Agency
Scottish regulator, Northern Ireland, Gibraltar, isle of man, Guernsey
Scientific journals and conferences
future water association
industry best practise networks
regulator networks
International and European technical groups
OHID dental fluoridation
World Health Organisation
water aid
future generations
water health partnership
public through inquiry service and complaints
food and drink manufacturers
professional institutes, e.g. institute of water, ciwem
colleges and skills development
Energy and utility skills
chemical products and fittings manufacturers
accreditation bodies standing committee of analysts UKAS and British standards
water regulations advisory scheme WRAS
Defra
The Inspectorate is a business unit in Defra’s Water and Flood Risk Management Directorate. As the independent regulator for drinking water quality, it is not directly responsible for development of policy, although the Chief Inspector has a statutory duty to report on quality matters to Ministers and advise the Secretary of State of any regulatory changes required. The Inspectorate actively engages with Defra on matters relating to water quality and sufficiency, resilience and water emergencies.
Engagement with Defra during the year also included the area of water resources ensuring that water quality concerns are considered fully in the determination of options to meet future demand, and various matters relating to sufficiency, demand management and water saving initiatives.
Ofwat and innovation
The Inspectorate has monthly liaison meetings with Ofwat to share information on company performance. It has worked together with Ofwat to develop common performance measures, to ensure the regulators are aligned. Common performance measures are in place for two water quality metrics: water quality contacts and compliance with regulatory standards. Companies receive penalty fines if their compliance risk index is worse than a set benchmark, based on industry performance.
The Inspectorate works with Ofwat to support innovation within the sector, whist ensuring consumers remain protected at all times.
RAPID
The Regulators’ Alliance for Progressing Infrastructure Development in Water (RAPID) was established to coordinate development and delivery of large-scale water resources infrastructure schemes, some of which will cross company boundaries, and improve resilience of supplies.
During 2024 the Inspectorate has continued to support RAPID to liaise with the Strategic Resource Options (SRO) sponsor companies, to ensure that all drinking water quality risks are being appropriately considered and appropriate mitigations identified as the schemes are being progressed. This has included assessing the first gate 3 submission for the Hampshire water transfer and water recycling SRO which was submitted in July 2024 with the draft decisions published in November 2024 and the final decisions published in February 2025.
The Inspectorate has also met with the SRO teams to discuss the progression of the development of the monitoring plans which feed into the strategic water quality risk assessments and drinking water safety plan development, as the schemes head towards their gate 3 submissions, and in the later part of 2024 worked closely with RAPID to help shape the PR24 RAPID scheme submission and assessment process.
Regulators Pioneer Fund – StreamLine project
The Drinking Water Inspectorate is one of three regulators along with Ofwat and the Environment Agency who have set up StreamLine to make it easier for innovators to obtain advice
Figure 44 – Streamline logo
The Environment agency
The Inspectorate has been engaging with the Environment Agency on drinking water protected areas, and it has a data sharing agreement where it sends the raw water data it received from companies to the Environment Agency for river basin management plans. The Inspectorate uses the environmental surveillance data to inform its regulatory policy, for example, to identify and inform water companies about which PFAS to include in their sampling and catchment risk assessments.
European regulators
The European Network of Drinking Water Regulators (ENDWARE) meets twice a year, hosted by rotating members, to discuss matters concerning drinking water quality. Topics include substances of emerging significance, and compliance with standards. Differing approaches to monitoring, analysis, and mitigation are shared for learning and awareness of best practice. Research findings may also be shared for awareness.
UK Health Security Agency
The Inspectorate liaises with the Health Security Agency as required, to address emerging issues and to seek advice on toxicology.
Fluoridation of supplies for dental health
Where water supplies are artificially fluoridated at the request of the Secretary of State for Health, the Inspectorate has worked with Office for Health Improvements and Disparities (OHID), through reviewing and commenting on fluoride results that fall outside the target range. The Inspectorate also supports OHID more widely on the technical and practical aspects of water fluoridation, including maintaining a code of practice for water companies, addressing Parliamentary Questions and enquiries from the public.
Drinking water safety – guidance to health and water professionals The Inspectorate has provided guidance for healthcare professionals in England and Wales on drinking water safety, which provides information on public and private supplies, the role of local authorities and the use of restrictions such as boil water notices, to protect public health.
The World Health Organisation
The Inspectorate has been redesignated as a World Health Organisation (WHO) Collaborating Centre for Drinking-water safety until 2026. (Ref UNK-232). This recognises the Inspectorate’s knowledge of implementing risk-based regulation in the field of drinking water supply, practically implementing the WHO water safety plan approach that was first promulgated as drinking water policy globally in 2004. An important function of our collaborating centre role is to provide support in the form of regulatory and technical knowledge through WHO organised workshops, training programmes, benchmarking projects, and research studies.
Consumer Council for Water
The Inspectorate shares and exchanges information with CCW on drinking water quality issues, with an emphasis on issues that directly affect consumers, through attending meetings and providing reports.
United Kingdom Accreditation Service
To maintain public confidence in drinking water sampling and analysis the Inspectorate collaborates with UKAS and other UK regulators (Drinking Water Quality Regulator for Scotland, and Department of Environment for Northern Ireland) to ensure that the sampling and analytical practices of water companies and the laboratories they use can be independently verified. In addition to meeting the requirements of ISO 17025, the Inspectorate and UKAS have published additional guidance for the water sector (Reference LAB 37), which makes specific requirements to ensure water companies meet their regulatory obligations.
Standing Committee of Analysts
The Standing Committee of Analysts comprises a series of working groups of experts in their fields, who provide guidance on methods of sampling and analysis for determining the quality of environmental matrices. Guidance is published as Blue Books within the series Methods for the Examination of Waters and Associated Materials. The guidance can be found on the SCA website: www.standingcommitteeofanalysts.co.uk.
The Inspectorate’s Chief Inspector is the current SCA strategic board chairman, which provides strategic direction for the organisation’s forward programme of work.
British Standards Institute
The Inspectorate assists and participates in the writing of British, European, and International standards that are associated to drinking water. This includes the analysis of drinking water, including quality control, drinking water products such as taps and thermostatic mixing valves, treatment chemicals and products, as well as general guidance standards such as temporary supplies.
Standardisation meetings may require attendance, but membership can be by email correspondence and comment. A committee meeting is generally held either annually or biannually.
Local authorities in England and Wales
The Inspectorate continues to support local authorities in their role as regulators of private water supplies by reviewing and updating guidance on implementing the Regulations where necessary, and producing topic focussed case studies and guidance as learning opportunities arise. The Inspectorate visited local authorities, to discuss challenges and developments in ways of working, and to see private supply types such as those used at temporary events. These visits help the Inspectorate to write its technical guidance, ensuring that guidance is practicable. The Inspectorate’s website has a dedicated area for private water supplies and the team maintain the guidance and resources made available to private water supply managers, users, and local authorities.
The Inspectorate is a member of the steering committee of the Water Health Partnership for Wales, and each year contributes to the Partnership’s annual conference by participating in exercises and delivering presentations.
The Chief Inspector produces two separate reports on private water supplies in England and Wales, to inform Ministers of their quality, and the impact of their regulation. The private water supplies team assess the data and information submitted by local authorities, including test results and risk assessment summaries to produce the statistics and disseminate messages and common learning.
Supply chain
The UK chaired the joint management committee of the four Member States group (4MS) with meetings in London, Berlin, and Lisbon. The 4MS is a voluntary group of countries including the UK, France, Germany, and the Netherlands, which works together on procedures for approval of materials and products in contact with drinking water with the intention of reducing the testing burden placed on industry by different approval schemes. The group has agreed to take forward a twin track approach, exploring opportunities for mutual recognition of existing approvals alongside the work already in hand on full harmonisation.
The Inspectorate has also responded to enquiries from and engaged with trade bodies, including the industry consortium for products in contact with drinking water. It has held two meetings with WRAS and Water UK on 4MS issues.
The Inspectorate also liaised informally with various supply chain members and representative bodies on drinking water supply matters.
Water Safe
The Inspectorate has a six-monthly liaison meeting with Water Safe and works collaboratively on campaigns. This year, it shared information on compliance breaches attributable to domestic plumbing, to enable Water Safe to promote safe practices and encourage the use of suitably trained plumbers.
Water quality standards advisory group
The function of the Drinking Water Inspectorate (the Inspectorate) is to protect public health and maintain public confidence in drinking water in England and Wales. The Inspectorate holds water companies to account to ensure they supply safe and clean drinking water, now and for future generations.
The Chief Inspector of Drinking Water has an advisory duty to the Secretary of State under Section 86(a)(ii) of the Water Industry Act 1991. In his letter to the Minister of July 2022, the Chief Inspector recommended a review of the list of the water quality regulations to address emerging risks and other contaminants. Over time, additional risks to drinking water quality have emerged due to the use of industrial chemicals and plastics, and the impact of climate change. Legacy issues, such as lead in older properties, remain.
Throughout 2024 the Inspectorate facilitated meetings of a group of experts convened by the Chief Inspector to review and advise on changes to the water quality regulations. The expert advisory group considered the scientific evidence, including toxicology and potential occurrence in drinking water supplies, of a defined list of 15 parameters, which included lead and per- and polyfluoroalkyl substances (PFAS). The review considered the addition, removal, tightening and relaxation of parameters to protect public health. International regulatory approaches were considered when evaluating the most appropriate options.
WIRED – Water Innovation – Regulators Exploring Data
The Inspectorate engaged with Ofwat and the EA in a joint project funded by the regulators pioneer fund to explore the use of data within the three organisations and how we could potentially share data between us in a safe and controlled manner to gain new insights into water company behaviour.
The basis for this was four design sprints and a one-day hackathon to investigate what may be possible should all three regulators decide to invest further into the ideas generated.
Annex A – Number of tests carried out by companies
Numbers in brackets reflect the number of active works, reservoirs or zones operated by that company in the region in 2024. Some companies are permitted to carry out some tests on samples taken from supply points, rather than from consumers’ taps
Company
Water treatment works
Service reservoirs
Consumer taps
Number of tests per company
Target number of tests
AFW
68,303(22)
31,381(40)
89,064(81)
188,748
188,858
ALB
0(0)
0(0)
879(2)
879
894
ANH
131,314(71)
78,493(116)
177,399(209)
387,206
389,836
BRL
17,540(12)
38,815(60)
33,856(34)
90,211
90,217
CAM
13,433(12)
5,985(14)
8,403(12)
27,821
28,000
ESP
0(0)
0(0)
5,859(11)
5,859
5,863
ICW
0(0)
0(0)
8,968(7)
8,968
8,978
ISC
1,685(7)
2,031(8)
1,968(13)
5,684
6,209
IWN
0(0)
0(0)
29,203(51)
29,203
29,203
LNW
0(0)
0(0)
14,050(27)
14,050
14,058
NES
58,337(43)
70,296(147)
137,951(127)
266,584
266,974
PRT
19,502(13)
7,809(4)
20,117(10)
47,427
47,462
SES
12,716(6)
7,112(5)
19,996(25)
39,824
39,824
SEW
72,940(63)
56,252(112)
83,496(74)
212,688
213,326
SRN
74,518(65)
55,562(71)
89,594(102)
219,673
219,723
SST
21,328(15)
6,384(14)
36,558(40)
64,270
64,300
SVT
114,865(87)
87,219(201)
227,506(266)
429,590
429,728
SWB
51,930(28)
71,166(126)
86,414(42)
209,510
229,733
TMS
92,867(79)
77,223(172)
261,521(261)
431,611
431,982
UUT
99,571(67)
87,673(159)
198,336(241)
385,580
387,474
VWP
808(1)
1,182(4)
600(0)
2,590
2,590
WSX
49,156(45)
81,388(138)
48,347(78)
178,890
178,932
YKS
86,074(47)
89,254(174)
210,475(109)
385,803
386,283
Total
3,632,669
3,660,447
Table 44 – Number of compliance tests carried out by water companies in 224
Sampling shortfalls
Water companies are required under regulation to take specific numbers of samples at their assets, the required number varies due to a number of factors, the Inspectorate assesses the shortfalls and discusses them with the company to arrive at an agreed position on the number of shortfalls the company had during the year.
Companies should expect greater scrutiny on their shortfalls in future reports as the Inspectorate is taking a greater interest in this area and will soon begin to track them more closely.
Company code
Agreed sampling shortfall
AFW
110
ALB
15
ANH
2,630
BRL
6
CAM
179
ESP
4
ICW
10
ISC
525
IWN
2,227
LNW
8
NES
390
PRT
35
SES
0
SEW
638
SRN
50
SST
30
SVT
138
SWB
20,223
TMS
371
UUT
1,894
VWP
0
WSX
42
YKS
480
Total
30,005
Table 45 – Agreed sampling shortfalls
Annex B – Compliance with standards
Microbiological compliance at water treatment works
Parameter
Standard
Total number of tests
Number of tests not meeting the standard
Number of tests not meeting the standard per company
Welton WTW – Post UV – Detection of Clostridium perfringens
Microbiological Contamination – Treatment works
4
160.177
SRN
Testwood WSW Plant failure & LOS
Planned work – Company staff
4
154.959
SRN
Brede WSW High Chlorate
Planned work – Company staff
4
134.473
SRN
Wingham WSW-Nitrates above PCV
Raw water deterioration
4
114.658
ANH
Welton WTW – Detection of Clostridium perfringens
Microbiological Contamination – Treatment works
3
97.197
SRN
Hastings LOS
Mains problem/ damage – Mains – Burst
4
80.684
TMS
Animal Ingress in Farnborough Service Reservoir
Structural failure – Service reservoir
3
62.767
SST
20″ Burst Main – Leabrook Road Wednesbury
Mains problem/ damage – Mains – Burst
1
53.599
SVT
Chester Taste and Odour
Raw water deterioration
4
45.798
SES
Cheam Loss of Supply
Failure of the contact tank outlet valve in the closed position following an unplanned works shutdown resulted in the inability to discharge treated water from the works.
1
34.016
ANH
Little Melton WTW E. Coli
Microbiological Contamination – Treatment works
3
33.186
SWB
Summercourt Burst Main
Mains problem/ damage – Mains – Burst
1
29.548
SRN
Testwood WSW – Enterococci detection
Microbiological Contamination – Treatment works
4
27.903
SRN
South Hill WSR Foreign Object
Other – Specify Below: Small lamp left in tank after inspection. Removed by ROV.
1
27.815
WSX
Langport White Water
Mains problem/ damage – Mains – Burst
4
26.075
ANH
Boughton Reservoir 3 – repeat coliforms
Microbiological Contamination – Treatment works
3
23.929
TMS
Reading Loss of supply
Loss of heating leading to freezing of assets. The event was prolonged due a run-to-waste decision that was based on a miscommunication over presence of a disinfectant residual and the lack suitable pumps to fulfil the run-to-waste decision.
4
20.265
SWB
Aerated Water Contacts in Truro Area
Emergency Work
3
18.856
SRN
Easton WSW Loss of Supplies following chlorine gas leak
Plant failure – Failure – Disinfection System
3
18.648
SRN
Twyford WSR Nitrate above PCV
Raw water deterioration
3
18.122
SRN
Baldslow WSR Ingress
Structural failure – Service reservoir
4
17.481
CAM
Euston WTW – Breach of disinfection
Plant failure – Failure – Disinfection System
4
17.382
CAM
Euston WTW – Breach of disinfection requirement
Plant failure – Failure – Disinfection System
4
17.382
WSX
Poole Trunk Main Burst
Mains problem/ damage – Mains – Damage by Third Party/Unknown
Unclear. some issues with PAC dosing, RGF operation and possible ingress, but no definitive cause.
4
13.952
SRN
Dyke Road Brighton WSR No1. Ingress
Structural failure – Service reservoir
4
12.406
SRN
Wigmore 2 WSR Tank Ingress
Structural failure – Treatment works
4
11.414
YKS
Longwood WTW loss of ferric dosing
Plant failure – Failure – Pumps
4
11.316
YKS
Middlestown/Horbury discolouration
Mains problem/ damage – Mains – Burst
3
10.518
WSX
Danesborough SR2 Enterococci
Satisfactory investigation, did not identify root cause
2
9.036
UUT
South Cheshire Discolouration
Discoloured water – cause unknown at present
2
8.682
NES
Tow Law Discolouration
Planned work – Company staff
4
8.451
LNW
Sufficiency of supplies – Park Views Epsom
Unplanned shut down of Cheam works on 15 December 2024, due to a faulty valve on the outlet of the contact tank
3
8.301
SRN
Brede WSW Harland Tank Ingress
Structural failure – Treatment works
4
8.068
IWN
Ebbsfleet – Water Outage
Leak located however valves on site not in fully open positions, causing low flows.
1
7.795
TMS
Media Interest in Beckenham, BR3
Increased illness contacts following publication of an article by the Guardian relating to water quality
1
7.565
IWN
Newmarket Road Do Not Use
Ground Contamination / Spillage – Hydrocarbon
4
7.416
TMS
Ufton Nervet WTW Turbidity Issue
Emergency Work
4
7.08
BRL
Frampton Cotterell discolouration
Planned work – company staff
3
6.73
Table 54 – Top 50 scoring events in 2024
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