Copyright in the typographical arrangement and design rests with the Crown.
This publication (excluding the logo) may be reproduced free of charge in any format or medium provided that it is reproduced accurately and not used in a misleading context. The material must be acknowledged as Crown copyright with the title and source of the publication specified.
Dedication
The Chief Inspector’s Report 2025 is dedicated to the memory of Maria Grace, who spent 40 years in the Civil Service, including the last 14 with the Inspectorate. Maria sadly passed away in February 2026 following a short illness. She was a highly valued colleague whose commitment to public service and consumers, together with her sense of humour, was greatly valued and will be sorely missed.
Glossary
Company code with its associated company name
AWI | Advanced Water Infrastructure Networks
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 | Last Mile Water Ltd
IWN | Independent Water Networks
ISC | Isles of Scilly
LNW | Leep Networks Water
MTX | Matrix Water
MUA | MUA Water Ltd
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
The provision of clean drinking water is fundamental to public health, wellbeing and economic prosperity, and access to clean water is recognised by the United Nations as a basic human right. Advances in water safety planning and systems management, underpinned by robust water quality regulation, continue to support some of the best drinking water in the world. Drinking water quality in Wales remains excellent, with public supplies consistently meeting the stringent regulatory standards for drinking water. Compliance with the standards in 2025 was 99.97%, providing strong assurance that consumers continue to receive wholesome water.
Drinking water supplies in Wales are protected through water safety planning, which provides a robust multi-barrier approach to preventing risks from materialising. Through this process, risks are identified from source to tap and appropriate mitigation is put in place before there is any deterioration in quality or sufficiency, or impact on consumers. The quality of supplies is further verified through extensive random sampling. Where things go wrong, the Inspectorate investigates, assesses compliance failures and events, and takes enforcement action where necessary to prevent recurrence. In 2025, regulatory activity highlighted the continuing importance of accurate risk assessments, representative monitoring, timely investigation and effective delivery of legal instruments.
The sector continues to face significant challenges. This report highlights the need for companies to improve asset health and resilience, with particular focus on air valves, distribution mains, treated water tanks and service reservoirs. Compliance risk in Wales remained elevated in 2025, driven by microbiological detections, turbidity and a continuing high number of iron-related failures. Events also demonstrated the importance of resilient alternative supply arrangements, effective tanker sampling, accurate asset records, reliable monitoring, and clear communication with consumers during incidents.
The report also shows that long-term improvement depends on companies moving from reactive operational responses to preventative, evidence-led management of risk. This includes stronger control of discolouration, improved management of lead and PFAS risks, more robust disinfection and treatment assurance, better understanding of asset condition, and sustained progress through transformation and enforcement programmes. Following the independent review of the water system in England and Wales, the Inspectorate is working with fellow regulators to realign the regulatory regime so that it better addresses climate change, population growth, new and emerging risks, national security and long-term resilience. This work will help lay the foundations for safe, secure and high-quality drinking water now and for future generations, balancing the needs of consumers while protecting the environment and public health.
Dr Marcus Rink OBE
Chief Inspector of Drinking Water
Introduction
Drinking Water 2025 is the annual publication of the Chief Inspector of Drinking Water for England and Wales. It is the 36th report of the work of the Inspectorate and presents the summary information about drinking water quality for the calendar year of 2025. It is published as an interim report 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 Wales. The industry dashboards for Wales 2025 are shown in summary below:
Figure 1 – Wales compliance dashboard
Water supplies and testing
This report sets out key facts about the quality of public water supplies in Wales. These supplies are provided by two water companies and one inset appointee, supplying more than 3.3 million consumers. An inset appointee is a supplier that replaces the incumbent monopoly provider for a defined site within that provider’s area. The area served by each water company is shown in figure 2.
Figure 2 – Company boundary map of Wales
Public water supplies
Key facts
Population supplied
3,313,500
Water supplied (L/day)
926,342,000
Treatment works
69
Service reservoirs
384
Water supply zones
103
Length of mains pipe (km)
30,616
Surface sources
257
Groundwater sources
42
Mixed water sources
1
Table 1 – Public supply key facts – data provided by water companies
Private water supplies
Key facts
Population supplied
104,431
Water supplied (L/day)
108,582
Number of supplies
14,902
Number of local authorities with private supplies
22
Supplies without a risk assessment
11,756
Table 2 – Private supply key facts – data provided by local authorities
The percentage compliance with the standards in the Water Supply (Water Quality) Regulations 2018 (‘the Regulations’) is shown in Table 3 below.
Parameter Group
% Compliance
Chemical Parameters
99.93
Indicator Parameters
99.98
Microbiological Parameters
99.99
Microbiological Parameters (Reservoirs)
99.97
Microbiological Parameters (Treatment works)
99.99
Pesticides
100
Overall
99.97
Table 3: Percentage of samples meeting the standards
Figure 3 – Compliance with the standards in 2025
Shortfalls
The number of samples required to be taken is specified in the regulations. In 2025 companies reported the following sampling shortfalls in table 4.
Company
Number of tests per company
Target number of tests
Number of sample shortfalls
Shortfall
Albion Eco
248
248
0
0%
Hafren Dyfrdwy
29,949
29,949
0
0%
Dŵr Cymru Welsh Water
263,830
264,319
489
0.19%
Wales overall
294,027
294,516
489
Table 4. Number of tests carried out by companies in Wales
Numbers in brackets reflect the number of works, reservoirs or zones operated by that company in Wales in 2024. Some companies are permitted to carry out some tests on samples taken from supply points rather than from consumers’ taps and therefore the number in brackets for consumers’ taps also includes supply points.
Advances in mapping technology have identified instances where samples were taken outside the correct zones. Where such issues were evidenced, the relevant companies were contacted and the affected samples were removed from the dataset on the basis that they were unrepresentative. In many cases, companies were also required to report these occurrences as formal events.
The Inspectorate will continue to scrutinise both the locations and frequency of sampling to ensure companies comply with regulatory requirements, including taking the correct number of samples at appropriate locations.
In parallel, the Inspectorate is reviewing the shortfall process, with the aim of introducing monthly automated updates to companies on their monitoring performance. This is intended to support sufficient, regular, and random sampling in line with regulatory expectations.
Compliance with the monitoring requirements set out in the Regulations remains consistently high in Wales. These requirements include the prescribed concentrations or values for parameters in drinking water, together with the required sampling frequencies and locations. This end-point verification provides broad assurance that supply systems are delivering water to consumers that meets regulatory requirements at the time and place sampled. However, company risk assessments continue to identify risks that are not fully controlled or mitigated. Where these risks are realised, they may result in a water quality impact, including a compliance failure or a notifiable event.
Where risks are realised, they may result in a compliance failure or a water quality event. The Inspectorate uses these outcomes to inform indices that assess the impact of failures and events, and the effectiveness of company actions to remediate risks and prevent recurrence. The Compliance Risk Index (CRI) measures the impact of compliance failures and their potential consequence for consumers. It is designed primarily as a regulatory tool to support proportionate scrutiny and ensure attention is directed to areas of greatest relative risk. Figure 4 shows company CRI performance.
In 2025, the Compliance Risk Index (CRI) for Wales remained elevated when compared with the wider industry. The three largest contributors to the Wales CRI score were coliform detections at Dŵr Cymru Welsh Water’s Court Farm and Bretton works, and a turbidity failure at Hafren Dyfrdwy’s Llandinam works. Dŵr Cymru Welsh Water recorded the highest CRI score in the industry at 7.1, while Hafren Dyfrdwy ranked 15th with a score of 1.253.
In total, Wales recorded three coliform breaches at treatment works and 18 coliform breaches and two Escherichia coli (E. Coli) breaches at service reservoirs in 2025. Eight of these breaches were covered by a Dŵr Cymru Welsh Water legal instrument, increasing the CRI score through the application of the relevant multiplication factor. Delivery of these legal instruments should secure improvements that reduce the likelihood of these risks recurring; once closed, the associated multiplication factor will no longer apply to the CRI score. In the context of increased regulatory scrutiny during transformation, the CRI for Wales is expected to remain elevated in the near term. This does not indicate a deterioration in drinking water quality, which remains excellent, but reinforces the importance of long-term strategic improvements to protect future supplies and manage risk.
Figure 2 shows variability in CRI for both Dŵr Cymru Welsh Water and Hafren Dyfrdwy since 2020, rather than a consistent trend.
Figure 4 – CRI scores for companies in Wales – last 5 years
Figure 5 shows the CRI for each company operating in England and Wales, broken down by site type: water treatment works, supply points, service reservoirs and zones.
Figure 5 – Industry Compliance Risk Index
The Compliance Risk Index (CRI) is not a statutory measure and does not override companies’ obligations to comply with prescribed concentrations or values under the Regulations. It is a risk-based regulatory tool used to prioritise attention and resources towards areas of highest relative risk. The CRI is also shared with Ofwat as part of a coordinated regulatory approach. A CRI target of 2 is used as the threshold for financial penalties, providing a consistent performance benchmark.
The industry median CRI in 2025 was 2.92, an increase from 1.77 in 2024 and 2.32 in 2023. Interpretation of the industry median should take account of two factors: company performance and the effect of regulatory intervention, where notices served in response to risk can amplify the score. Dŵr Cymru Welsh Water recorded the highest company CRI score in 2025. This is of concern, although the amplification associated with transformation notices should also be considered.
Figure 6 shows the CRI scores, removing the multiplication factor caused by having live legal instruments applied to the asset which had the failed test. It also shows that the impact of the legal instruments has reduced in 2025 meaning fewer failed tests are at locations where improvements are already in-flight. This is a positive step change in the right direction, and should continue if the company maintains delivery of legal instrument milestones and outcomes.
Figure 6 – CRI over past 5 years – CRI scores in blue, CRI scores removing legal instrument multiplier in green
In 2025, the CRI for companies wholly or mainly operating in Wales was 6.73. This represents a deterioration from 4.08 in 2024, following an improvement from 7.257 in 2023. The overall CRI comprises scores from different parts of the water supply system, including treatment works, supply points, service reservoirs and zones.
At company level, Dŵr Cymru Welsh Water’s CRI improved from 7.736 in 2023 to 4.28 in 2024, before deteriorating to 7.1 in 2025. Hafren Dyfrdwy’s CRI increased from 0.112 in 2023 to 1.10 in 2024, and to 1.26 in 2025. Dŵr Cymru Welsh Water accounted for a significant proportion of the Wales CRI and exceeded the Wales overall CRI of 6.73. CRI enables the key contributors to each component of the score to be identified, helping to show where risks originate, as illustrated in Figure 7.
Figure 7 – Wales Compliance Risk Index for 2025
When comparing with the national picture, it can be seen that the greatest compliance risk is coliform detections in zones, with the secondary driver being iron failures in zones.
Figure 8 – Top 10 parameters by site
In Wales, breaches at large works supplying a high number of consumers continue to make a substantial contribution to the annual CRI score. In 2025, 39% of the total CRI score arose from three breaches, at Court Farm works, Llandinam works and Bretton works. This represents an increase on previous years, where high-scoring breaches occurred at Bretton works in 2024, Felindre works in 2023, Ponsticill works in 2022, and Felindre works and Court Farm works in 2021. Non-compliance at large works carries a higher relative risk because of the number of consumers supplied. Coliforms are indicator parameters and require precautionary action by companies to ensure the continuing protection of consumers.
In 2025, iron contributed 40% of the total CRI score in Wales, compared with 7% in 2024 and 33% in 2023. Although the proportion of the CRI score attributable to iron can vary depending on the scoring of other breaches, including those at large works, the number of iron breaches in Wales remains high: 17 in 2025, 13 in 2024, 14 in 2023 and 21 in 2022. Further detail on discolouration is included later in this report.
In total, there were 23 microbiological breaches at treatment works and service reservoirs in Wales in 2025, excluding E. coli detections. This was an increase from 14 breaches in 2024. Service reservoir breaches are considered in more detail later in this report.
Learning from compliance failures
In 2025, Wales recorded several microbiological compliance breaches. A consistent theme across these breaches was insufficient asset resilience, particularly the inability to remove critical tanks from supply for timely internal inspection due to the absence of bypass arrangements and/or contingency options. In several cases, investigations were delayed for many months where assets were operationally critical, limiting confidence that consumers were not exposed to ongoing risk at the time of failure. These cases reinforced the need for proactive resilience planning to ensure that microbiological investigations can be completed promptly under all operating conditions.
Failures at service reservoirs and treated water tanks highlighted weaknesses in inspection regimes, asset condition knowledge, and record accuracy. Several breaches demonstrated the importance of maintaining accurate and up‑to‑date schematics, particularly following asset commissioning or decommissioning, to ensure investigations are comprehensive and sampling strategies are appropriate. Notably, issues were identified in both ageing assets and newly commissioned infrastructure, emphasising that construction age alone does not equate to low risk.
At consumers’ taps, a microbiological breach was attributed to inappropriate sampling point selection. The presence of tap attachments compromised the representativeness of samples, leading to misleading results and unnecessary regulatory action. This reinforced the requirement for clear sampling criteria, staff awareness, and assurance that consumer tap samples accurately reflect supply water quality.
Sporadic taste and odour breaches continued in 2025, driven primarily by recurring raw water precursor compounds and treatment‑related by‑products. While operational mitigation measures were in place, several repeat events indicated that initial controls were not sufficiently robust. Improvements to granular activated carbon (GAC) management, including more conservative exhaustion targets, represent a positive step toward more effective and sustainable control of aesthetic risks.
Iron and discolouration failures remained widespread, with Wales continuing to perform poorly relative to companies in England. The majority of iron breaches were linked to deteriorating cast iron mains, low turnover, dead ends, and inaccuracies in asset records, particularly where closed valves were not reflected in GIS systems. While flushing programmes provided short‑term compliance, they frequently failed to address underlying causes, and in some cases sampling undertaken post‑flushing was not representative of typical network conditions. The Inspectorate consistently emphasised the need to shift from reactive flushing toward timely asset renewal and long‑term investment planning.
A turbidity breach at a borehole pumping station highlighted the importance of effective treatment control and monitoring. The absence of a final water turbidity shutdown contributed to the event, prompting improvements to shutdown arrangements, monitor calibration and proactive maintenance. The incident reinforced the need to protect the full disinfection stage and to ensure that any impacts from chemical dosing on turbidity and pH are adequately controlled.
Overall, the 2025 compliance picture in Wales reinforces the need for stronger asset resilience, accurate records, representative monitoring and proactive investment. Recurrent reliance on reactive measures and short-term compliance sampling provides limited assurance of sustained water quality. Addressing root causes through improved governance, long-term planning and preventative maintenance remains essential to reducing repeat failures and protecting consumers.
Microbiological detections at works and service reservoirs
In Wales, there were three microbiological compliance failures at water treatment works in 2025, all at Dŵr Cymru Welsh Water assets. A recurring theme across several failures was the inability to remove assets from supply for timely investigation due to insufficient asset resilience. There has been a steady increase in microbial failures in Wales since 2021 as can be seen in Figure 9. The following paragraphs describe some of these failure scenarios along with lessons learnt.
Treatment works
Parameter
Current standard
Total number of tests
Number of tests not meeting the standard
Number of tests not meeting the standard by company
Table 5. Microbiological tests – The number of tests performed and the number of tests not meeting the standard
Turbidity – indicator is a critical control parameter for water treatment and disinfection.
Service reservoirs
Parameter
Current standard
Total number of tests
Number of tests not meeting the standard
Number of tests not meeting the standard by company
E. coli (confirmed)
number/100 mL
20,057
0
–
Total coliforms (confirmed)
number/100 mL
20,057
0
DWR (10), HDC (2)
Table 6 – Microbiological failures at service reservoirs
Consumers’ taps
Parameter
Current standard
Total number of tests
Number of tests not meeting the standard
Number of tests not meeting the standard by company
Coliform bacteria (indicator)
number/100 mL
8,703
30
HDC(4), DWR(26)
E. coli (confirmed)
number/100 mL
8,703
1
DWR(1)
Enterococci (confirmed)
number/100 mL
753
0
–
Table 7 – Microbiological failures at consumers’ taps
E. coli and Enterococci at treatment works, service reservoirs and consumers’ taps
Company
E. coli in water leaving treatment works
E. coli in water leaving service reservoirs
E. coli at consumers’ taps
Enterococci at consumers’ taps
ALE
0 – 0
0 – 0
0 – 12
0 – 4
DWR
0 – 11,166
1 – 16,189
1 – 8,067
0 – 638
HDC
0 – 942
1 – 3,868
0 – 624
0 – 111
Table 8 – Detection of E. coli and Enterococci at treatment works, service reservoirs and consumers’ taps
Note: Results are shown as the number of positive tests followed by the total number of tests
Figure 9 – Microbiological failures over last 10 years
In February, Dŵr Cymru Welsh Water reported a single coliform in a sample collected from Court Farm works final water. The company was unable to identify a root cause, and the Inspectorate was therefore unable to conclude that recurrence was unlikely. Further investigation was deferred until contact tanks and final water tanks could be removed from supply for internal inspection. Due to the critical role of the works in maintaining supplies within the South East Wales Conjunctive Use System during a period of drought, this work was not completed until 21 October 2025, approximately eight months after the breach. Roof flood testing identified no points of ingress and all tanks were reported to be in satisfactory condition.
Similarly, in April, a single coliform detected at Alaw South works required inspection of multiple tanks; however, this was delayed until Cefni works could support supply resilience. At Bretton works, resilience limitations were more acute, with a single-compartment contact tank and no bypass preventing removal from supply following detections in May 2024 and May 2025, delaying internal inspection until October 2025. These examples demonstrate how insufficient resilience and lack of operational flexibility can significantly delay investigations into microbiological risks.
Further cases highlight the importance of asset knowledge and comprehensive investigation processes. At Dŵr Cymru Welsh Water’s Pengarnddu service reservoir no. 3, a coliform detection in July 2025 was not fully investigated due to incomplete schematics, which omitted hydraulic links to an adjacent reservoir, and limited resilience prevented removal of the asset from supply. At Porthmadog service reservoir, outdated schematics incorrectly included a decommissioned works and omitted an active source, complicating the investigation following confirmation of E. coli.
At Cruigau service reservoir, where tankering was used to support demand during hot weather, multiple coliform detections occurred in both the service reservoir and associated tankers within the same period; however, tankering was not initially considered within the investigation. Structural and ingress issues were also identified at several sites. At Axton service reservoir, insects entered through a damaged membrane, despite the roof previously passing a flood test. At Birchgrove service reservoir, internal inspection identified significant ingress through roof joints and a nearby sinkhole, neither of which had been evident during the previous inspection in November 2024.
These examples demonstrate recurring weaknesses in inspection regimes, schematic accuracy, and the consideration of operational activities and changing environmental conditions as contributors to contamination pathways. At Hafren Dyfrdwy’s Hirnant service reservoir, inspection identified deteriorated seals, non-compliant hatch arrangements and vegetation overgrowth. These events demonstrate the need for a systematic and resilient approach to managing microbiological risk across water supply systems. Companies should ensure that critical assets can be taken out of service promptly through appropriate bypass arrangements and alternative supply options, enabling timely inspection and investigation.
Accurate and up-to-date maps and schematics are essential to support effective incident response and must be maintained when assets are commissioned, modified or decommissioned. Investigation procedures should consider all credible sources of contamination, including operational activities such as tankering and network changes. In addition, inspection regimes should not rely solely on flood testing, but incorporate comprehensive structural, visual and condition-based assessments to identify latent defects. Strengthening resilience, improving asset knowledge and enhancing investigation practices will reduce delays, improve root cause identification and support the consistent supply of wholesome water under both normal and abnormal operating conditions.
Image 11 – Birchgrove reservoir with roof joint ingress evident.
Chemical and physical parameters
Parameter
Units
Total number of tests
Number of tests not meeting the standard
Number of tests not meeting the standard per company
Colour
mg/L Pt/Co
3225
1
HDC(1)
Odour
Dilution number at 25°C
3222
5
DWR(5)
Taste (quantitative)
Dilution number at 25°C
3220
5
DWR(5)
Hydrogen ion (pH) – indicator – zone
pH Value
3220
Sulphate
mg/L SO₄
460
Sodium (total)
mg/L Na
749
Nitrate (total)
mg/L NO₃
751
Nitrite – consumers taps
mg/L NO₂
751
Ammonium (zone)
mg/L NH₄
929
Aluminium (total)
µg/L Al
3188
Iron (total)
µg/L Fe
3188
17
DWR(16) HDC(1)
Manganese (total)
µg/L Mn
3190
1
DWR(1)
Copper (total)
mg/L Cu
749
Fluoride (total)
mg/L F
460
Arsenic (total)
µg/L As
749
Cadmium (total)
µg/L Cd
749
Cyanide (total)
µg/L CN
459
Chromium (total)
µg/L Cr
749
Mercury (total)
µg/L Hg
458
Nickel (total)
µg/L Ni
749
Lead (10)
µg/L Pb
747
2
DWR(2)
Antimony
µg/L Sb
749
Selenium (total)
µg/L Se
749
Pesticides (total by calculation)
µg/L
725
Polycyclic aromatic hydrocarbons (total by calculation)
µg/L
752
Residual disinfectant – free
mg/L
8897
Residual disinfectant – total
mg/L
8261
Electrical conductivity
µS/cm at 20°C
2997
Boron
mg/L B
458
Benzo[a]Pyrene (total)
µg/L
754
Tetrachloromethane (total)
µg/L
466
Trichloroethene & Tetrachloroethene – sum of 2 substances (total by calculation)
µg/L
464
Trihalomethanes (total by calculation)
µg/L
754
1,2-Dichloroethane (total)
µg/L
468
Benzene (total)
µg/L
468
Bromate
µg/L BrO₃
581
Gross alpha
Bq/L
1
Gross beta
Bq/L
1
Tritium
Bq/L
1
Total
–
Table 9 – The number of tests performed and the number of tests not meeting the standard
Hafren Dyfrdwy reported a final water turbidity failure of 1.25 nephelometric turbidity units (NTU) at Llandinam New Borehole Pumping Station on 20 February. The company’s investigation concluded that the most likely root cause was the presence of undissolved solids associated with lime dosing at the treatment works. Analysis of historical data trends, catchment risk assessments and ultrafiltration membrane performance indicated that the failure was not attributable to deterioration in raw water quality from the Llandinam boreholes.
At the time of the breach, no final water turbidity site shut‑down was operational. In response, the company installed a final water turbidity site shut‑down upstream of the lime dosing point. This was initially set at 0.95 NTU and subsequently reduced to 0.75 NTU on 18 March. In addition, the balance tank dosing chamber (high‑lift sump) was scheduled for cleaning to minimise the accumulation of lime deposits.
The company increased the calibration frequency of the final water turbidity and pH monitors and adopted the draining and cleaning of lime storage tanks as an annual proactive maintenance activity at Llandinam BPS.
Companies are reminded that site shut‑down arrangements should be configured to protect the entirety of the disinfection stage, from the point of disinfectant application through to final water sampling. Alarms and shutdowns should be subject to routine testing regimes to provide assurance of operation. Where chemicals are applied within the disinfection stage, their potential impact on downstream disinfection performance, including effects on turbidity and pH, should be continuously assessed and controlled to ensure compliance with company disinfection policy targets.
Lead
Lead is a toxic metal that can dissolve into drinking water when it comes into contact with lead pipes. Consumers are largely protected from exposure through phosphate dosing, a widely used treatment across many zones in Wales that reduces plumbosolvency. This approach is one of the key reasons why few, if any, consumer tap samples fail the lead standard each year. Additionally, the relatively low number of required lead tests under the Regulations contributes to this outcome.
In 2025, there were two lead failures in Wales, both in Dŵr Cymru Welsh Water’s area and both reported at 11 µg/L. The failure in East Anglesey identified lead solder and a lead communication pipe at the property, alongside failures in orthophosphoric acid dosing. Remedial work was undertaken at the property, and the company was advised to investigate the root cause of the dosing failure and review the maintenance regime.
At the second failure, in Barry, the company’s inspection identified that the supply pipe was made of lead and was therefore the likely cause. Flushing advice was provided and the customer was advised to replace the supply pipe.
Taste and odour
Taste and odour in drinking water are key indicators of consumer acceptability and confidence, and are regulated under the requirement that water must be wholesome and clean. Under drinking water legislation, taste and odour are indicator parameters, meaning that while they are not typically associated with direct health risks at the levels encountered, any deterioration may signal underlying issues with source water quality, treatment processes, or distribution system condition.
Unacceptable taste or odour may arise from a range of causes, including algal activity in source waters, the presence of naturally occurring organic compounds, treatment inefficiencies, or the mobilisation of deposits within the distribution system. Chlorine and chlorinous compounds can also influence taste, particularly where dosing is elevated or poorly controlled.
Where concerns are identified, they require investigation under regulation 18 to determine the cause and extent of the issue. Persistent or widespread complaints may indicate deficiencies in treatment optimisation, asset performance, or network management, and require corrective action to restore consumer confidence.
Companies are expected to monitor and manage taste and odour proactively through effective control of treatment processes, maintenance of distribution systems, and appropriate response to customer reports. These parameters are also considered within regulation 27 risk assessments to ensure that water remains not only compliant but acceptable to consumers.
There were five taste and five odour failures in Wales in 2025, a decrease from 12 in 2024, as shown in Figure 8.
Dŵr Cymru Welsh Water’s Bontgoch zone continued to feature prominently among failing zones, with seven of the 10 failures recorded in this zone.
There have been recurring taste and odour breaches, detected by the company laboratory taste and odour panel, in this water supply zone since January 2020. Investigations have identified elevated concentrations of 2,4,6 trichloroanisole in the supply from Bontgoch works, with sources likely to include both naturally occurring compounds in the raw water and formation as a chlorination by-product during treatment. While laboratory analysis has detected taste and odour and confirmed the presence of this compound, consumers at affected properties have not typically reported abnormal taste or odour. The company has engaged external specialists and implemented a range of mitigation measures, including filter disinfection to remove biomass and associated by-product formation potential, and enhanced monitoring linked to pre-second stage chlorination. Third stage filters downstream of the contact tank are also due to be decommissioned and bypassed by June 2026 as part of longer-term treatment improvements.
In the Abergele and Rhyl water supply zone, a taste breach on 28 January 2025 was attributed to elevated concentrations of 2-methylisoborneol (MIB) in raw water feeding Glascoed works. A similar taste and odour event with the same root cause had occurred in May 2024. Although mitigation measures, including powdered activated carbon dosing and blending with Llanerch borehole supplies, were implemented following the earlier event, these controls were not sufficient to prevent the subsequent breach. Investigations identified that granular activated carbon contactors at Glascoed works were operating sub-optimally due to excessive ferric coagulant dosing, which reduced MIB removal efficiency. The company has since identified the need for front-end acid dosing to optimise coagulation and improve granular activated carbon performance, with delivery planned by March 2027. In the interim, enhanced monitoring, blending strategies and revised granular activated carbon management, including more conservative exhaustion criteria, have been implemented to improve control.
The Inspectorate noted that the recurrence of a taste event within eight months of a previous occurrence indicates that initial mitigation measures were not sufficiently robust. However, it also recognised that additional controls and enhanced surveillance have since been implemented to enable more responsive optimisation of treatment in line with changes in raw water quality. The adoption of improved granular activated carbon management processes is expected to strengthen removal of taste and odour compounds across relevant treatment works.
These breaches highlight the importance of implementing robust, sustainable control measures for taste and odour risks, particularly where raw water sources are prone to seasonal or persistent contamination. Companies should ensure that treatment processes are fully optimised and resilient to variation in raw water quality, with a clear understanding of how upstream processes impact the performance of downstream assets. Monitoring programmes should be sufficiently sensitive and responsive to detect deterioration early and inform timely operational adjustments. Where previous events have occurred, mitigation measures should be critically evaluated to ensure they are effective in preventing recurrence. Strengthening process control, asset performance and proactive risk management will support the consistent delivery of acceptable water quality to consumers.
Figure 12 – Taste & odour failures since 2016
Iron
Figure 13 – Iron breaches since 2018
In the Dŵr Cymru Welsh Water Barry and Sully water quality zone, an iron breach was linked to a closed valve that was incorrectly recorded as open on the company’s mapping system, creating a dead leg and allowing sediment to accumulate. A similar issue was identified in the Malpas, Caerleon and Cwmbran zone, again caused by incorrect asset status on GIS records following valve operations. In response, the company has introduced a standardised, web-based process to improve communication between operational and office teams and ensure network records reflect the live status of assets. These cases demonstrate the importance of accurate asset information in preventing avoidable water quality failures. Several failures were associated with deteriorating cast iron mains and low network turnover. In the Sketty and Gower area, an iron exceedance followed a burst and was linked to heavy tuberculation in an unlined main with low flow, requiring ongoing flushing and investigation. In Cardiff and Rumney, repeated flushing and temporary measures, such as trickle caps, were used to restore compliance. However, samples taken following these interventions were not representative of underlying network conditions at the time of the failure, compromising root cause investigation. Internal inspections confirmed extensive corrosion in a 1912 cast iron main, yet no renewal has been prioritised. Similar issues were identified in Hereford, Newport West and North Anglesey, where sediment accumulation at dead ends or within ageing trunk mains caused repeated or high-risk failures. In Hereford, repeated failures persisted despite flushing, prompting a business case for longer-term investment, while in North Anglesey an oversized, corroding trunk main continues to present an ongoing risk.
Figure 14 – Sketty/Gower zone breach reactive main cut-out.
Other cases further emphasise the limitations of short-term operational responses. In Pencoed and the Bridgend Valleys, iron failures were attributed to sediment build-up in trunk mains, with flushing undertaken while longer-term investment options were considered. In Malpas, Caerlon and Cwmbran zone a manganese failure was due to a shut valve creating a dead end in the distribution network promoting sediment build up.
Across these events, flushing has commonly been used as the primary mitigation measure, often supported by monitoring and maintenance programmes. In several cases, low-velocity maintenance flushing programmes have been put in place to increase local main turnover. Dŵr Cymru Welsh Water has recently committed to a greater focus on sediment removal flushing, using higher velocities to systematically clear accumulated sediment from its networks. It should be noted that sediment removal and scouring velocities are not always achievable with the available assets and operational conditions, for example where internal tuberculation has reduced original internal pipe diameters. While these actions can provide temporary improvement, they do not address the underlying causes, particularly where mains are structurally degraded or poorly configured hydraulically. In some cases, flushing may also disturb deposits and increase short-term risk if not carefully controlled and validated through representative sampling.
These breaches demonstrate the need for a more proactive and strategic approach to managing discolouration risk. Companies should ensure that asset records accurately reflect operational status at all times, supported by robust processes for updating systems following field activities. There should be clear short, medium and long-term strategies for addressing iron risks, including timely consideration of asset renewal where infrastructure condition limits the effectiveness of operational controls. Reliance on reactive flushing and compliance sampling alone does not provide assurance of sustained water quality, particularly where samples are taken under artificially improved conditions. Effective risk management requires representative monitoring, understanding of hydraulic conditions, and targeted investment to remove root causes, ensuring the consistent supply of wholesome and acceptable water to consumers.
Figure 15 – Dŵr Cymru Welsh Water iron breaches
Colour
Colour in drinking water is an important indicator of aesthetic quality and treatment performance. It can originate from the raw water source, particularly where natural organic matter such as humic substances is present, as well as from metals like iron and manganese or disturbances within the distribution system. While not a direct health concern, elevated colour may indicate underlying operational issues and can affect consumer confidence, and it is therefore expected to be maintained at levels acceptable to consumers.
A colour breach was reported in Hafren Dyfrdwy’s concessionary supplies zone. The property is supplied from a spring source, with water piped to the property and treated by a point-of-use ultraviolet treatment system. A permanent boil water notice is in place at the kitchen tap. Although the company services the ultraviolet system, the disinfection process is not monitored or validated. The company recognises that deterioration in raw water quality, including elevated colour, may reduce the effectiveness of point-of-use ultraviolet treatment. The same property also recorded a colour breach in February 2024. Concessionary supplies in this zone are due to be connected to a mains supply in 2026 under notice HDC-2022-00001, and the company has reported that it remains on track to complete this work. As a precautionary boil water notice remains in place, and permanent connection to mains supply is due by the notice completion date.
Learning from events
There were 65 events notified to the Inspectorate in 2025. Thirty-two of these were single-property incidents, 16 of which related to consumers’ distribution systems and were therefore outside the control of the water company.
Figure 16 – Water quality events in Wales
The most significant event related to regulation 31 approval for Dŵr Cymru Welsh Water, with an Event Risk Index (ERI) score of 5,299. By comparison, the highest scoring event in 2024 had an ERI of 240. Regulation 31 events can attract large ERI scores due to the size of the potentially affected population and the duration of the event, which may extend over a considerable period while unapproved products remain in situ before they are identified and removed.
The second highest ERI score was recorded by Albion Eco, at 657, for a loss of supply event following an upstream mains burst. In this case, the small supplied population of 180 meant that the ERI score was proportionately higher than it would have been for a similar event affecting an incumbent company, as the entirety of the company’s supplied population was affected. Figure 11 shows ERI for Wales in 2025. The bars show the individual company ERI scores, the Wales line is ERI for the companies combined to one, the ERI median line is the median company ERI.
Figure 17 – ERI score per company
Figure 18 – ERI over 5 years
Figure 19 – ERI score for each company in England and Wales
Figures 20 and 21 show the number of events in Wales and across the industry respectively. In Wales there is no discernible trend, however the last two years have seen a peak similar to the previous peak within the charted 25 period. Further analysis of the nature of the events causing these peaks would be required to determine any pattern or commonality.
Figure 20 – Wales ERI and median ERI – Total scores for each company
Figure 21 – ERI scores in Wales compared to the rest of the industry
Company code
Event name
Cause of event
Final classification
Final event assessment
ERI score
DWR
Regulation 31 Approval
Use of unapproved materials/products
3 (Significant)
Prosecution considered
5,298.682
ALE
Broughton Mains
Mains problem/ damage – Mains – Burst
3 (Significant)
Recommendations made
657
DWR
Aston Burst
Mains problem/ damage – Mains – Burst
3 (Significant)
Enforcement-legal instrument
245.807
DWR
Bryn Cowlyd WTW Loss of Supply
Mains problem/ damage – Mains – Burst
4 (Serious)
Recommendations made
164.335
DWR
Cardiff Discolouration
Depressurisation of network following false high readings on level probe at Cefn Mabley SR leading to level dropping below top of outlet main. Discolouration but no loss of supply.
3 (Significant)
Enforcement-legal instrument
30.856
DWR
Llanrumney Burst Main
Mains problem/ damage – Mains – Burst
2 (Minor)
Enforcement-legal instrument
3.631
DWR
Carmarthen Loss of Supply
Mains problem/ damage – Mains – Burst
3 (Significant)
Enforcement-legal instrument
3.026
DWR
Gower/Swansea Discolouration
Mains problem/ damage – Mains – Burst
3 (Significant)
Suggestions made
1.57
DWR
Rhyl Discolouration
Mains problem/ damage – Mains – Burst
2 (Minor)
Suggestions made
1.564
DWR
Swansea Discolouration
Mains problem/ damage – Mains – Burst
2 (Minor)
No recommendations or suggestions made
0.807
Table 10 – Top 10 scoring events notified in 2025
Specific events
DWR – Regulation 31 approval
A routine regulation 31 compliance assessment, undertaken in relation to materials intended for use in a planned capital scheme, identified that products supplied and installed within the public distribution network between 12 June 2024 and 27 August 2024 did not hold valid approval during that period. The company confirmed that neither the product composition nor the instructions for use had changed between the lapse in approval and subsequent reapproval. A risk assessment carried out by the company concluded that the associated risk to water quality was therefore low.
To support this conclusion, the company completed surface area calculations for typical fittings across the likely installed size range. These calculations indicated that the fittings met the exemplar criteria set out in Advice Sheet 8, and this was submitted as evidence to demonstrate that the risk to supplied water quality remained low. However, the company was initially unable to determine the exact specifications or installation locations of the fittings but has since carried out retrospective analysis and determined a population of 1,123,195 were impacted out of a total company population of 3,093,158.
The company has acknowledged that the installation of unapproved products occurred. While the company maintains that the risk to water quality was low, it was unable to fully substantiate this assessment due to the absence of detailed records relating to fitting types and precise installation locations. Recommendations were given requiring a critical review of procedures concerning record keeping, regulation 31 compliance assurance, and the methodology used for surface area calculations to demonstrate exemplar status.
Companies should ensure that systems are in place to prevent the use of products that do not have regulation 31 approval, the critical point in time being when water goes into supply.
ALE – Boughton loss of supply event
Following an upstream burst on a Dŵr Cymru Welsh Water main, the potable supply to Shotton Mill was lost from 14:00 on 14 August 2025 until 20:00 on 16 August 2025, a total interruption of 51 hours. During this period, the company implemented contingency measures to maintain water availability on site by providing an alternative supply from the separate, partially treated, non potable industrial system fed from Dŵr Cymru Welsh Water Ashgrove Water Treatment Works.
The industrial supply is dosed with sodium hypochlorite at Shotton Mill to maintain a free chlorine residual of 0.1 ppm, intended solely to suppress biological growth within the site’s industrial distribution network. Under normal operating conditions, the potable and non potable systems are entirely separate. However, to maintain water availability for welfare facilities during the incident, a single cross connection was installed, and the potable system was temporarily primed with the non potable supply.
The company provided trend data demonstrating total chlorine residuals, although free chlorine residuals were not evidenced, within the system over the period. Outlet turbidity, conductivity and pH data from online instrumentation at Ashgrove works were also supplied. Turbidity and conductivity remained within regulatory limits, while pH tracked marginally above the Schedule 2 minimum value of 6.5.
To protect consumers on site, the company issued Do Not Drink advice, displayed notices at all outlets, and provided bottled water as an alternative drinking supply.
Following restoration of the potable supply on 16 August 2025, the company removed the temporary cross connection (restoring the air gap separation), undertook flushing to achieve eight turnovers of the calculated system volume, and converted the Do Not Drink advice to Boil Water advice on 17 August 2025 pending satisfactory sample results.
Sampling surveys were conducted at site taps on 18 August 2025 for microbiology analysis and on 19 August 2025 for a full suite of water quality parameters. All results were satisfactory.
Companies are reminded that the wholesomeness requirements of regulation 4 apply to all domestic uses of water, including handwashing in welfare facilities, and that suitable sampling should be conducted to verify that supplied water meets this regulatory requirement. Further, the timing of the issuing and rescinding of any restriction of use advice should be based on a dynamic risk assessment verified through appropriate sampling.
DWR – Aston burst main
A burst occurred on the rising main supplying water from Bretton Works to Aston service reservoir (SR). An initial repair attempt was unsuccessful, resulting in the service reservoir emptying and causing a significant loss of supply to customers in the Deeside area. During the incident response, water tankers were deployed; however, no samples were taken from the tankers themselves. Water quality sample failures were subsequently recorded in areas downstream of tanker infusion points, and it remains unclear whether these failures were attributable to the burst event, to tanker operations or both.
The treatment works was restarted, and the service reservoir and wider network were recharged in a controlled manner. Adequate bottled water supplies were provided to affected customers throughout the incident.
A number of deficiencies were identified during the review of the event. These included the absence of a water quality risk assessment for the use of an overland temporary main, insufficient assessment of the robustness of the initial repair, contributing to a secondary burst and an extended loss of supply, and the lack of in‑situ turbidity monitoring during flushing activities. In addition, no in‑situ water quality check records were available, and none of the deployed tankers were sampled; only the fill point and downstream properties were sampled, with downstream failures recorded.
Recommendations have been given to address these deficiencies and strengthen future operational and water quality assurance processes.
The incident highlights the need for robust water quality assurance and risk assessment during emergency response activities, particularly when using tankers or overland supplies. Effective incident management must include thorough assessment of repair robustness to prevent escalation, clear water quality monitoring and recording during flushing and tanker operations, and routine sampling of tankers themselves to ensure risks are adequately controlled and can be clearly distinguished from underlying network failures.
DWR – Bryn Cowlyd works loss of supply
An event in North Wales in January 2025 left more than 114,000 people without a water supply for seven days. Dŵr Cymru Welsh Water’s Bryn Cowlyd works supplies the North Wales coastal area, including Conwy, Llandudno and Colwyn Bay. On 13 January, a potential leak was identified on the works outlet main. A walk of the main identified a leak under the Afon Ddu and the company began planning the repair. Before this could take place, a power outage in the early hours of 15 January resulted in an automatic shutdown of the works. When a restart was attempted, the outlet main failed to reach the required pressure and it was concluded that the works could not be restarted until the main had been repaired. The areas normally supplied by Bryn Cowlyd works subsequently experienced loss of supply over seven days while the main was repaired and the system refilled. This affected a population of 114,562 people, or 47,734 properties, supplied either directly from the gravity system from Bryn Cowlyd final water tank or by service reservoirs also supplied by the works.
Due to its location beneath a river, the repair of the main was challenging and required a large excavation to provide safe access. Once exposed, the company identified a pinhole leak that had eroded a coupling, creating a hole of approximately 50–75 mm.
Figure 22
Figure 23
Figure 24
Alternative supplies in the form of tankers, Arlington tanks and bottled water were deployed to provide a water supply to the affected population until normal supplies were restored.
The loss of supply generated local and national media interest, with reports of consumers collecting sea water to flush their toilets as they were unable to access sufficient alternative supplies for this purpose.
Once the main had been repaired and the works restarted, the company encountered further complications with elevated turbidity in the final water tanks, which served to provide required contact time to achieve full disinfection. In addition, samples collected from the works final sampling point prior to return to supply were deemed unrepresentative of the water from the tank. The company received a recommendation to collect a suite of samples on return to supply, to validate its risk assessment that the water was wholesome and adequately disinfected. Other recommendations were also made in relation to sampling, including sufficient sampling for Cryptosporidium, as the one sample collected during the event was unable to be analysed due to debris on the slide.
During the event, the company used 27 tankers to retain or restore supplies to consumers over the seven-day period, with 390 discharges made. Nine samples were collected from these tankers during the event, significantly below the requirements of regulation 6 of the Regulations, which requires tankers to be sampled at the point of discharge and during each subsequent 48-hour period. Prior to the event, the Inspectorate had served a regulation 28(4) notice on the company for alternative supplies, due in part to procedures and resources being insufficient to allow adequate sampling. While the company is working towards compliance with regulation 6 and the notice, events will continue to score higher on the Event Risk Index. The Inspectorate’s enforcement team is monitoring the company’s progress against the legal instruments.
DWR – Cardiff discolouration
On the evening of 11 March 2025, pressure and flow alarms were activated in the Cardiff area downstream of the Cefn Mabley service reservoir. Subsequent investigation identified that the water level in compartment 2 of the reservoir was 2.5 m, significantly lower than the 3.5 m indicated by telemetry. No associated reservoir level alarms, rate‑of‑change alerts, or flow deviation alarms had been generated. The reduced reservoir level resulted in partial depressurisation of a downstream trunk main and discolouration within the affected water quality zones.
At the time of the incident, compartments 1 and 1A of Cefn Mabley service reservoir were out of service for maintenance in accordance with the company’s tank inspection notice (ref. DWR‑2021‑00002). Telemetry data analysis enabled the company to trace the issue back to the service reservoir within two hours of the initial alarm activation.
Customer communication was undertaken through mass text messaging, telephone calls, and website updates. Sampling surveys were deployed across the affected area to assess water quality impacts, and bottled water was proactively supplied to vulnerable consumers. The defective level probe at Cefn Mabley service reservoir was replaced, a secondary level probe installed, and manual level monitoring implemented for the duration of the incident.
A company‑wide review of service reservoir level probes was subsequently completed, with remediation or contingency plans established for any probes found to be outside tolerance or inaccessible. The investigation identified a discrepancy between the written SR inspection procedure and the inspection form used on site, specifically regarding the requirement to verify level probe accuracy during inspections. This procedural inconsistency, combined with the absence of level verification and water quality checks during the earlier transfer of water from in‑service compartment 2 to out‑of‑service compartment 1, represented potential missed opportunities to prevent the incident.
The incident demonstrates the importance of reliable reservoir level monitoring and fully aligned inspection procedures, as failures in telemetry accuracy, alarm configuration, and verification processes—particularly during periods of reduced operational resilience—can lead to undetected loss of service reservoir volume, downstream water quality impacts, and missed opportunities for early intervention.
DWR – Llanrumney burst main
At approximately 15:00 on 3 September 2025, Dŵr Cymru Welsh Water was alerted, via pressure and flow alarms, to a burst on a 15‑inch trunk main in the Llanrumney area of Cardiff. The company implemented its established emergency planning arrangements, drawing on existing area and activity action plans, and acted swiftly to mitigate the impact on consumers.
Within the first twelve hours of the incident, two bottled water stations were established, bottled water was distributed to vulnerable consumers, tankers were deployed for network infusion, repairs were initiated, and rezoning measures were implemented to minimise the extent of the supply interruption. The repair was completed and the main recharged during the early hours of 4 September 2025.
The incident attracted local media interest, and the company provided regular progress updates to the press. Some deficiencies were identified in the alternative supplies’ response, particularly regarding tanker sampling in accordance with Regulation 6. However, overall, the company’s operational response effectively limited the impact on consumers and restored supplies in a timely manner.
To provide assurance against the requirements of SEMD, companies should focus on creating and exercising appropriate emergency plans for large-scale trunk main bursts of this nature. These plans should be designed to minimise supply disruption, protect consumer confidence and control water quality impacts.
DWR – Carmarthen loss of supply
A significant loss of supply event affecting the area east of Carmarthen occurred between 12 and 14 July 2025. The event was initiated by a burst on a 21-inch trunk main from Brondini service reservoir, detected at 04:49, with the burst located shortly afterwards. Initial risk assessments indicated up to 6,500 properties could be affected; however, operational mitigation, including rezoning, tankering and deployment of an overland main, reduced the number of properties without supply to 290 on the first day and 59 by 13 July. Repairs were completed on 14 July and supplies were fully restored. A total of 96 ‘no water’ contacts and one water quality contact were reported during the event.
The Inspectorate concluded that, although supply interruptions were managed to minimise consumer impact, there were deficiencies in water quality control and event reporting. It is likely that water supplied during the event may have been unwholesome, with elevated iron concentrations and reports of a ‘bitter’ taste identified in tanker samples, albeit unaccredited taste tests. There were also procedural gaps, including incomplete sampling of tankers discharging into the network and a failure to promptly withdraw a tanker following an adverse test result. In addition, information relating to sampling, tanker operations, and overland main commissioning and disinfection was not fully reported.
Companies should ensure that robust and consistently applied operational controls are employed during emergency supply arrangements, particularly where tankers and overland mains are deployed. Companies should also ensure that all alternative supply assets are fully risk assessed, disinfected, sampled and documented, and that adverse results trigger immediate and decisive action. Accurate and complete event reporting, including consumer contacts and operational data, is essential to demonstrate compliance and support learning. Strengthening these areas will reduce the risk of supplying unwholesome water and improve resilience during loss of supply events.
DWR – Gower/Swansea discolouration
A significant discolouration event affecting the Gower area of Swansea occurred between 15 and 16 October 2025, following a burst on a 20-inch steel trunk main. A small leak identified on 9 October progressively worsened and resulted in a major burst, which was isolated in the early hours of 15 October. The burst occurred as a result of a longitudinal split adjacent to a previously installed repair collar. Network flushing and controlled flow reduction were implemented to manage the impact, and the main was fully repaired by 20:00 on 16 October. While no loss of supply occurred and positive pressure was maintained, 45 consumer contacts relating to discolouration were received. Sampling identified failures for iron, turbidity and manganese at four properties on 15 October, although resamples taken the following day were satisfactory, demonstrating that water quality was restored promptly.
The Inspectorate concluded that the company supplied water that exceeded prescribed concentrations for turbidity, iron and manganese, rendering it unwholesome and in breach of regulation 4(2)(c) of the Regulations. However, it noted that the operational response was timely and effective, with coordinated actions between network and production teams reducing discolouration risk and facilitating repair. Mitigation measures included controlled reductions in treatment works output, flushing of affected mains, and in situ checks (although turbidity monitoring was not undertaken during flushing). The Inspectorate welcomed the proactive mitigation approach and effective verification prior to returning the network to supply, while also recommending that historic repairs are more explicitly considered within leak detection, risk assessment and prioritisation processes.
Companies are encouraged to consider the importance of proactive and risk-based management of trunk mains, particularly where historic repairs and emerging leaks coincide. Companies should ensure that risk assessments incorporate asset history to prioritise intervention and prevent escalation to burst events. Operational responses should include comprehensive real-time monitoring, including turbidity, alongside coordinated network control and verification prior to returning assets to service. Maintaining sufficient critical repair materials and embedding learning from trunk main reviews will strengthen resilience and reduce the likelihood and impact of discolouration events.
Figure 25 – Deterioration of the leak
Figure 26 – Deterioration of the leak
Figure 27 – Deterioration of the leak
Figure 28 – Leaking repair collar adjacent to longitudinal split on the main
DWR – Llanrumney do not drink
A significant event occurred in Llanrumney, Cardiff on 17 October 2025, where ‘do not drink’ advice was issued to 20 properties. The event followed a sediment removal flush during which a valve, previously recorded incorrectly on the GIS system, was opened without appropriate risk assessment. This allowed stagnant water to enter the distribution main, leading to multiple consumer contacts reporting discolouration, unusual tastes and odours, and one report of gastric illness. The valve was re-isolated on the same day and restrictions remained in place until 29 October 2025, when satisfactory sampling results enabled the advice to be lifted.
The Inspectorate concluded that the company supplied water that exceeded prescribed concentrations for a range of parameters including metals, turbidity, hydrocarbons and polycyclic aromatic hydrocarbons, and therefore the water supplied was unwholesome. Deficiencies were identified in operational control and incident response, including failure to undertake a suitable risk assessment prior to valve operation, delays and limitations in the initial sampling strategy, and a lack of early recognition of potential polyaromatic hydrocarbon (PAH) contamination despite consumer reports indicating petrol-like odours. The sampling approach, which followed mains flushing, reduced the likelihood of capturing representative worst-case water quality, and this was considered a breach of regulatory requirements. The Inspectorate also identified shortcomings in determining the extent of the affected area and in the timely and consistent application of ‘do not drink’ advice to consumers.
The event highlights the need for robust risk assessment and control of network operations, particularly when altering valve configurations or undertaking flushing activities. Companies should ensure that asset condition, operational history and data accuracy are fully considered before interventions, and that sampling strategies are designed to capture representative water quality at the earliest stage of an event. Early recognition of contamination risks, particularly where multiple consumer indicators suggest chemical contamination, should trigger an appropriately escalated response. Strengthening these areas, alongside improved processes to define and protect the affected population, will reduce the risk of supplying unwholesome water and improve the effectiveness of response to water quality incidents.
HDC – Market Street Llangollen do not drink
A significant event occurred in Llangollen on 11 December 2025, involving the issue of ‘do not drink’ advice to six properties following the detection of elevated lead concentrations. The event developed from earlier sampling in June and July 2025, which identified lead within a shared supply serving eight properties. Flushing advice was initially provided; however, further sampling in December identified an elevated 2-minute flush result at one property, triggering the escalation to ‘do not drink’ advice. Investigations identified that the shared communication pipework comprised mixed materials, including MDPE, copper and galvanised pipe, with some properties remaining on restrictions into January 2026 due to ongoing access and replacement challenges.
The Inspectorate concluded that water supplied during the event exceeded the prescribed concentration for lead and was therefore unwholesome in breach of regulation 4(2)(b) of the Regulations. While the company had undertaken risk assessments and mitigation actions, these did not fully capture the extent of the lead risk or prompt sufficiently protective responses at earlier stages of the investigation. Delays were identified in confirming pipework materials and in sampling all properties on the shared supply. The Inspectorate also highlighted that the potential contribution of galvanised pipework to lead exceedances, including via galvanic action, had not been fully considered. Recommendations were made to improve procedures for pipe material verification, strengthen lead risk assessments, and consider clearer triggers for escalation to ‘do not drink’ advice.
Companies are encouraged to ensure a precautionary and systematic approach to managing lead risks, particularly on shared supplies with uncertain or mixed pipe materials. Companies should ensure that all connected properties are promptly identified, sampled and protected where elevated results are detected, and that physical verification of pipework materials is undertaken at the earliest opportunity. Risk assessments should explicitly consider mechanisms such as galvanic corrosion and the presence of galvanised pipework, and clear escalation criteria should be in place to trigger protective advice. Strengthening these practices will reduce the risk of prolonged consumer exposure to lead and improve the effectiveness and timeliness of incident response.
Figure 29 – causes of high ERI scores in Wales
Consumer contacts
Acceptability of water
The acceptability of drinking water is consistently ranked by consumers as a high priority. It can be affected by several factors, including appearance, such as discolouration or aeration, and taste or odour. Most acceptability complaints relating to black, brown or orange discolouration are associated with raised concentrations of manganese, iron and aluminium.
Although these metals are rarely present at concentrations harmful to health, they can cause widespread rejection of water on the basis of appearance. Consumers expect their drinking water to be clean and safe, and discolouration events can be highly disruptive and reduce confidence in supply. The Inspectorate takes these events seriously and many companies have regulation 28(4) notices in place to address 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 more detailed consumer contact information, including:
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 national grid reference (easting and northing) of 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);
and if the contact is associated with a notifiable event, and the event reference number associated with it.
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 by companies in 2025, covering 2024, was the first submission to include this additional information. Direct year-on-year comparisons for the new data are therefore not yet possible. To maintain continuity of a comparable dataset and monitor industry performance and progress, only primary contacts and non-event contacts have been used in reporting acceptability data for 2024. When a meaningful dataset is available, further analysis will be undertaken to provide additional insight into consumer contacts.
In Wales in 2025, there were 8,161 consumer contacts regarding the appearance, taste and odour of drinking water, reported to companies wholly or mainly operating in Wales. This equates to a rate of 2.46 contacts per 1,000 population. Table 8 shows the number of contacts received for each complaint type for Welsh companies, with contacts relating to discoloured water, including brown, orange and black water, being the most common reason.
Category
Number of contacts
Wales contact rate per 1000 population
Industry contact rate per 1000 population
Appearance – Brown Black Orange
5,149
2.46
Taste / Odour – Other
894
Appearance – White Air
676
Drinking water quality concern – Lead and analysis
503
Taste / Odour – Chlorine
501
Appearance – Particles
340
Illness – Gastroenteritis
339
Appearance – General Conditions
204
Appearance – White Chalk
147
Taste Odour – Earthy Musty
132
Illness – Skin
102
Appearance – Blue Green
64
Illness – Oral
38
Taste / Odour – Petrol Diesel
37
Illness – Medical Opinion
23
DWQ Concern – Incident Related
20
Appearance – Animalcules
17
Drinking water quality concern – Lifestyle
5
Drinking water quality concern – Pets Animals
4
Drinking water quality concern – Campaign
0
Total
9,195
Table 11. Water quality complaints in Wales, 2025
Discoloured water
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. Dŵr Cymru Welsh Water has had a company-wide notice in place since 2022, with six individual zonal notices remaining from AMP7. 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 in these areas.
The number of contacts reporting discoloured water, including brown, orange or black water, across the industry in England and Wales has decreased over recent years. This improvement now appears to have stalled, with deterioration reported in 2024, when the rate was 0.49 contacts per 1,000 population, and almost no improvement in 2025, when the rate was 0.48. This equates to 29,959 contacts across the industry in 2025 regarding black, brown and orange water. In Wales, this stagnation is also apparent, with a notable deterioration in 2024 and no sustained improvement over the past five years. The rate in Wales was 1.55 contacts per 1,000 population in 2025.
Figure 30 – Welsh company and industry discolouration rates 2016 to 2025
The 2025 rate of 1.55 contacts per 1,000 population in Wales is significantly higher than the industry average of 0.48. Of the Welsh contacts, 98.3% were from consumers served by Dŵr Cymru Welsh Water. The company remains the worst performing company in the industry for discolouration and has held this rank since 2014, as shown in Figure 31.
Figure 31 – Rate of discolouration contacts by company in 2025 (excluding Isles of Scilly and inset companies)
The contact rate for Hafren Dyfrdwy, which had been showing an improvement, has stalled in recent years (Figure 32). The company’s rate remains under the industry average.
Figure 32 – Welsh company and industry discolouration rates 2016 to 2025
Figure 31 shows where the Welsh companies rank over the whole industry for discolouration contact performance in 2025.
Dŵr Cymru Welsh Water remain an industry outlier and although the deterioration in 2024 was improved upon in 2025, there has been no overall improvement in rate in the past five years. Dŵr Cymru Welsh Water had a number of zone-specific discolouration notices and a companywide notice for discolouration. Three of the zone-specific notices have been delayed into AMP8. The companywide notice was served in 2022 with a target of 1.4 contacts per 1,000 population to be achieved by the end of AMP7. Figure 33 shows that the company fell short of this target. When there was an early indication that this target would not be met, the Inspectorate engaged with the company to better understand why the company believed this was the case by critically evaluating how the company determined its deliverables and the resulting impact. Part of this ongoing notice included setting a new target for the end of AMP8 using the same methodology as that for the AMP7 target. The company’s new target is 1.08 contacts per 1,000 population.
Figure 33 – Welsh company and industry discolouration rates 2016 to 2025
Dŵr Cymru Welsh Water remains an industry outlier for discolouration. Although performance improved from the deterioration seen in 2024, there has been no overall improvement in the contact rate over the past five years. The company has a number of zone-specific discolouration notices and a company-wide notice for discolouration. Three of the zone-specific notices have been delayed into AMP8. The company-wide notice was served in 2022 with a target of 1.4 contacts per 1,000 population to be achieved by the end of AMP7. Figure 15 shows that the company did not meet this target. Following early indications that the target would not be achieved, the Inspectorate engaged with the company to understand the reasons, including how deliverables had been determined and what impact they were expected to have. A new AMP8 target has been set using the same methodology as the AMP7 target. The company’s new target is 1.08 contacts per 1,000 population.
In addition to the overall black, brown and orange contact rates described above, several consumer complaints received by the Inspectorate in 2025 were prompted by persistent and unresolved discolouration of supply. To assess the impact of ongoing discolouration on consumer confidence, three cases reported in the Dŵr Cymru Welsh Water area in 2025 are considered below. Taken together, these cases highlight persistent challenges in managing discolouration, maintaining consumer confidence, and delivering effective investigative and operational responses.
Across all cases, consumers reported ongoing aesthetic water quality issues, primarily discolouration and, in some instances, odour, leading to rejection of supply. While the company implemented a range of mitigation measures, the Inspectorate consistently identified shortcomings in investigation quality, sampling adequacy, and response timeliness.
Overall, the findings point to systemic pressures within the industry, particularly in relation to ageing assets, network management practices, and complaint handling processes. Regulatory conclusions emphasise the need for more proactive, evidence-based, and customer-focused approaches to both investigation and resolution.
One case involved long-term, intermittent discolouration affecting a localised supply area, with repeated consumer contacts over several years. Mitigation measures included reactive turnover flushing, the introduction of a routine flushing programme, and installation of an inline supply filter. However, investigative activity remained limited, with only a small number of samples taken despite the persistence of issues.
Although sample results demonstrated compliance with regulatory standards at the time of testing, the continued presence of visible discolouration meant the supply remained unacceptable to the consumer. The Inspectorate concluded that the measures taken had not addressed the underlying cause or provided sufficient reassurance.
A second case concerned a long-running complaint in an urban network involving both discolouration and odour, with initial contacts dating back several years. Early investigative activity was limited, and opportunities to undertake timely sampling and identify root causes were missed. A more comprehensive investigation was only initiated following later water quality failures identified during the water quality zone’s routine compliance sampling process, at which point elevated iron concentrations were identified.
The underlying cause was attributed to ageing infrastructure and low network turnover, which contributed to sediment mobilisation and aesthetic failures. Although mitigation measures, including enhanced flushing and monitoring, were eventually implemented, delays and investigative deficiencies prolonged the impact on consumers.
The third case involved a multi-year group complaint affecting several properties in a rural network. Consumers reported persistent discolouration alongside pressure and supply issues over an extended period. Sampling confirmed elevated iron and turbidity, while the network itself was characterised by ageing iron mains in poor condition with significant sediment accumulation.
A range of operational interventions, such as flushing programmes, supply rezoning, and installation of point-of-use filters, were implemented. However, these measures did not deliver sustained improvement, highlighting the limitations of short-term mitigation in the absence of fundamental infrastructure renewal.
Across all cases, the condition of distribution assets, particularly ageing iron mains, was identified as a primary driver of discolouration (figure 34). Low flow conditions and hydraulic disturbances were found to mobilise accumulated sediments, resulting in recurring water quality failures. These issues were especially acute in network extremities and areas with limited turnover.
The Inspectorate also identified consistent deficiencies in investigation and sampling practices. Sampling was frequently delayed, insufficient, or not representative of actual conditions. Repeat complaints did not consistently trigger escalation or enhanced investigation, and opportunities for early intervention were missed, allowing issues to persist over extended periods.
Operational mitigation measures, such as flushing and point-of-use filters, were widely used but provided only temporary mitigation. Flushing improved water clarity in the short term (Image x) but did not prevent recurrence, while filters addressed symptoms at individual properties rather than systemic causes. In some cases, flushing activities themselves risked worsening conditions by mobilising accumulated sediments.
Communication with consumers emerged as another critical area for improvement. Delays in providing updates and test results reduced consumer confidence, while explanations of root causes and mitigation measures were sometimes incomplete or inconsistent. As a result, consumers remained unconvinced of the safety or reliability of the supply despite regulatory compliance in many instances.
These cases reinforce regulatory expectations that water companies must undertake timely and representative sampling, apply risk-based investigation methods that consider upstream network factors, and implement robust systems to identify and escalate repeat complaints. Failure to meet these expectations is likely to result in increased regulatory scrutiny.
The repeated identification of infrastructure condition as a root cause highlights the need for accelerated asset investment. Targeted mains replacement in high-risk areas, improved management of network extremities, and better integration of asset condition data into water quality planning are all necessary to achieve sustained improvements. In several cases, infrastructure renewal has been identified as the only effective long-term solution.
More broadly, the findings reflect wider industry performance pressures. Elevated discolouration complaint rates and ongoing regulatory interventions indicate that systemic improvements are required. There is growing expectation that companies demonstrate measurable progress in both operational performance and customer outcomes.
The complaint assessments outlined above reveal consistent patterns of operational and structural challenge in maintaining water quality within distribution networks. While steps have been taken to address individual issues, responses have often been reactive and insufficient to resolve underlying causes. Persistent discolouration, combined with delayed or inadequate investigation, has led to prolonged consumer dissatisfaction and reduced confidence in supply.
The Inspectorate’s findings point to the need for a step-change across the industry. This includes more rigorous and timely investigations, effective escalation of repeat complaints, improved transparency in consumer communication, and sustained investment in infrastructure to address root causes.
Taken together, these cases demonstrate the importance of moving from reactive discolouration management towards proactive, system-wide improvement in both technical performance and customer assurance.
Figure 34 – Discoloured water at a consumer’s property.
Figure 35 – Colour grading during a flushing operation
Taste and odour
As with discoloured water contacts, the industry rate for total taste and odour contacts has gradually reduced over time, although it worsened in 2024 and 2025 to 0.27 contacts per 1,000 population. In Wales, the rate was almost double the industry rate, at 0.47 contacts per 1,000 population in 2025, and has remained broadly stable, with no sustained progress over the last decade.
Figure 36 – Rate of taste and odour contacts in Wales
Earlier in this report, examples of investigations into taste and odour compliance failures were described. These instances do not necessarily result in, or directly correlate with, consumers contacting their water company. Consumer contact data therefore provides a useful reflection of direct consumer experience and offers an alternative insight to that provided by compliance failures. General taste and odour, and chlorine-related contacts, feature prominently across the years shown in Figure 36. While it is not realistic to expect all consumer contacts to be eliminated, the lower industry rate in England, including companies with similar source and network characteristics, indicates that further mitigation of the causes of these contacts is achievable.
Asset health
Treated water tanks and service reservoirs
During 2025, there were three coliform compliance failures at water treatment works and 18 at service reservoirs. There were no E. coli detections at treatment works and two at service reservoirs. Ingress into contact tanks and service reservoirs remains a recurrent issue and represents a residual risk, as these results demonstrate.
Companies are expected to understand and maintain their assets through a programme of physical inspections, which may be supplemented by inspections using remotely operated vehicles. The Inspectorate considers physical inspections necessary because they provide clarity and better resolution than remotely operated vehicle inspections and enable cleaning of walls and structures within the reservoir during the same isolation and drain-down activity. Although 10 years is the maximum interval advised in the Principles of Water Supply Hygiene for treated water storage, the Inspectorate recommends that inspections are carried out more frequently on a risk-based basis.
The Inspectorate has increased scrutiny of service reservoirs and tanks, including through the service reservoir and tanks data return, to assess the quality of inspections and the robustness of remedial works. Analysis of the most recent dataset highlights continued weaknesses in inspection frequency, with 195 tanks out of 6,312 nationally not having been inspected for more than 10 years. In Wales, the combined figure is eight out of 815 reservoirs. This represents a significant overall improvement compared with the initial data return in 2021, which showed 457 tanks overdue or with no inspection record across the industry, including 50 in Wales. However, reservoirs continue to represent an area of risk requiring attention.
Company code
Number of tanks inspected within 10 years
Number of tanks in supply overdue inspection (>10 years)
Total number of tanks
Percentage of tanks overdue inspection (>10 years)
HDC
112
7
119
5.88%
DWR
692
1
693
0.14%
Wales total
807
8
815
0.98%
Table 12 – Overdue service reservoir inspections – Data has been calculated from the industry returns.
Figures 37 and 38 show progress made by Dŵr Cymru Welsh Water and Hafren Dyfrdwy. There are eight at-risk tanks that have not been fully inspected in the past 10 years, a slight increase from the previous year. Seven of these tanks are covered by separate regulation 28(4) notices, and four require a new tank to be constructed before the existing tanks can be removed from service. A short-term measure in these notices is the use of remotely operated vehicle inspections to provide information on current internal tank condition and integrity.
Figure 37 – DWR tanks data
Figure 38 – HDC tanks data
Figure 39 shows a comparison with other companies in the industry in 2026. The tank inspections that Dŵr Cymru Welsh Water have completed since the regulation 28(4) notice was put in place in 2022 have greatly improved their position and they now rank fourth in terms of percentage of assets at risk.
Hafren Dyfrdwy rank 14th in the industry in 2026. Although the overall number of tanks overdue an inspection has decreased, their overall ranking within the industry has not improved. This slow progress can be partially explained by the longer time frame over which it will take to construct the new tanks which are required in to remove four tanks overdue for inspection.
Figure 39 – total number of assets per company
Water safety planning and risk assessment
The Inspectorate’s Risk Assessment team is responsible for understanding risks to water quality and sufficiency, adapting to new mitigation requirements, and developing approaches to Drinking Water Safety Planning (DWSP).
During 2025, the team assessed substantial volumes of data and documentation submitted by companies. Through systematic review of risk lines uploaded through regulation 28 reporting, the team strengthened its understanding of how effectively risks to water quality and sufficiency are being managed across the industry. This work enables the Inspectorate to identify where action is required and to support companies in complying with regulations 27 and 28 through DWSP audits, individual line assessments of regulation 28 data, and legal instrument closure audits. Collectively, these activities help maintain and improve risk management practice across the water industry.
The Risk Assessment team continues to engage with industry through the quarterly DWSP Forum, providing updates on current work and addressing issues raised by water companies and NAVs. To further support consistent implementation of DWSP requirements, the team has also introduced liaison meetings with companies and NAVs to provide additional support and guidance.
DWSP Guidance
In July 2025, the Risk Assessment team published the Guidance on risk assessment and risk management specific to Drinking Water Safety Plans (DWSPs) following collaboration with water companies through the Drinking Water Safety Planning Forum and a small in-person working group convened to resolve outstanding issues. The guidance provides a comprehensive framework for the delivery of a DWSP and introduced a new category, category J, for recording carried-forward risk. The introduction of category J is to enable consistent reporting of categories and methodology for carrying risk scenarios forward to downstream stages across the industries water supply systems and will be a requirement from February 2027. This increases the fairness of scoring within the Risk Assessment Risk Index (RARI) used to indicate companies’ current and trending risks.
Alongside this change to reporting categories, the use of hazardous events is being further endorsed by the Inspectorate through the DWSP guidance so that there is better clarity regarding root cause analysis and control measure/mitigation application for risks. Using hazardous events contributes to understanding risk scenarios at an asset, stage and cumulative supply system level to give a more accurate representation of potential risk to water quality and quantity at the consumer tap.
Sufficiency
In September 2024, the National Infrastructure Commission (now NISTA) published its report, Developing Resilience Standards in UK Infrastructure. In response, the Inspectorate sought to assess the extent to which companies understood their own sufficiency and resilience arrangements and wrote to them in December 2024 requesting further information.
The Risk Assessment team initially reviewed companies’ regulation 28 reports to determine which sufficiency-related risks had been reported to the Inspectorate and what mitigation measures were in place. However, this review proved inconclusive due to variations in the way companies reported hazardous events, with some companies not reporting sufficiency risks at all.
Consequently, the team drew on the three key recommendations set out in the NISTA report and requested this information from all water companies and new appointments and variations (NAVs). The responses provided an evidence base to inform the development of guidance on the delivery of a draft water sufficiency guidance in late 2025. The team has since revised the Sufficiency Guidance so that it aligns with the principles of DWSPs and this will be published in 2026.
Per and polyfluoroalkyl substances (PFAS)
Following the Inspectorate’s PFAS guidance issued in August 2024, companies were required to monitor 6:2 FTAB (6:2 fluorotelomer sulphonamide alkyl betaine), which was added to the list of PFAS parameters, and to report the ‘Sum of PFAS’ from January 2025.
The above monitoring requirement was extended to New Appointments and Variations (NAVs) also. The NAVs are also expected to exchange information and data and to maintain a forward-looking PFAS strategy. Annex C of the Information Direction lists all PFAS chemicals of interest. Companies are also required to notify the Inspectorate if additional PFAS chemicals not listed are identified at concentrations above tier 1.
The PFAS guidance was updated in March 2025, Information Letter 03/2025, to provide further detail on PFAS tiers and associated actions, alongside requirements for monitoring and reporting, regulation 27 risk assessments, regulation 28 reporting, and company PFAS strategies. The updated guidance also set out expectations for bulk supplies, including those involving NAVs.
Audits
Through DWSP audits, the Risk Assessment team has continued to identify recurring issues in the way companies record risks, contributing to inconsistency across the industry and an ongoing reliance on reactive rather than proactive measures to reduce risks.
Companies should take a proactive approach to identifying and addressing risks, rather than waiting for issues to emerge before considering investment needed to protect public health. A reactive approach weakens the effectiveness of risk management and makes it harder to compare risk profiles across companies.
Companies must strengthen their DWSP arrangements to support the early identification and management of risks, thereby protecting public health and securing compliance with regulatory parameters, rather than relying on retrospective action in response to water quality or sufficiency issues. Companies must also ensure full compliance with regulations 27 and 28. To date, the majority of DWSP audits have resulted in ‘minded to enforce’ decisions and/or the issue of legal instruments requiring companies to review regulation 27 risk assessments and regulation 28 reporting.
Due to reduced team capacity, substantial input into legal instruments arising from audits undertaken in 2024, and wider internal Inspectorate commitments, this was the only onsite audit carried out in 2025. Other programmed audits were rescheduled to 2026.
RAR Reporting and Company Breakdown of DWI Categories
The annual submission of companies’ regulation 28 data took place in October. Companies used the Inspectorates’ online portal for this year’s submission including uploading of their DWSP methodologies and declaration with Director sign off. Any issues experienced with this process were easily resolved with good communication from companies and input from the Inspectorate’s Data Management Team.
Companies’ risk assessment record (RAR) data is submitted using the DWI categories shown with definitions in the table below [table RA1]. Companies must apply DWI categories appropriately to allow data to be meaningful and to give clarity in risk management.
DWI category
Description
A
Target risk mitigation achieved, verified, and maintained
B
Additional or enhanced control measures which will reduce risk are being validated
C
Additional or enhanced control measures which will reduce risk are being delivered
D
Additional or enhanced control measures are required to materially reduce risk
E
Risk under investigation
F
Partial mitigation
G
No mitigation in place: control point downstream
H
No mitigation in place and none required
I
Future risk not requiring mitigation at present
J
No mitigation in place, carried forward risk: control point upstream
X
Line no longer relevant.
Table RA1 – DWI categories
Risk Assessment Risk Index (RARI)
The risk assessment risk index (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, either by indicating this 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 since 2019. 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 in line with the DWSP Guidance, gaining a more consistent approach over the coming years. This includes the introduction of category ‘J’ for carried forward risks. Category J will not be included in the RARI calculations at this time, however it will allow for a more consistent approach within the industry to category application across company supply systems in the future.
Figure RA1 – company average RARI scores
Top 10 current identified risks in Wales
Category I is used to indicate perceived future risks that may need to be investigated and mitigated. Such risks include hazards that may be associated with climate change, emerging contaminants, 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.
Top 10 current identified risks in Wales (as a % sum of industry RARI)
The top three perceived risks remain the same as recorded in 2024, however the perception of these risks have increased, with the remaining being similar to last years figures.
Figure RA2 – top 10 risks
Poly and perfluoroalkyl substances (PFAS)
PFAS are a group of man-made compounds based on chains of carbon and fluorine atoms. They contain at least one fully fluorinated methyl or methylene group. The carbon-fluorine bond is very strong, meaning these compounds do not degrade easily in the environment. They are resistant to grease, oil, water and heat, and have been used in a wide range of products, including stain- and water-resistant fabrics and carpets, paints, firefighting foams, cookware and food packaging.
The production, use and disposal of these substances means they are now widely detected in the environment. Because of their persistence, they may eventually be found in water, including groundwater and surface water.
The Inspectorate updated its guidance to industry in August 2024 on requirements to submit sample results and summary risk assessment information for PFAS, and this remains a major focus. Companies have continued targeted sampling strategies focused on sites most likely to be at risk from PFAS contamination. In 2025, companies across the industry collectively carried out more than 666,000 analyses for individual PFAS. In total, more than 2.3 million analyses have been performed since 2012, providing a significant dataset to support understanding of the challenges for drinking water. Analysis peaked in 2024, when more than 777,000 tests were carried out. The reduction in 2025 reflects a more focused and targeted sampling programme based on validated risk assessments.
PFAS tiers are now applied to any PFAS chemicals of interest detected in the final or raw water. PFAS chemicals of interest are identified in the parameter list (Annex C of the Information Direction). The actions companies should be taking for the three tier levels is available in our most recent guidance – DWI_PFAS-Guidance_Mar_2025.pdf
Sites are classified as:
Tier 1 where PFAS concentrations are <0.01 µg/L.
Tier 2 where PFAS concentrations are <0.1 µg/L.
Tier 3 where PFAS concentrations are ≥0.1 µg/L
Monitoring by water companies 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 practicable. 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.
Analysis targets source water because this provides information on the hazard and informs the mitigation required, whether through blending, removal of the source water or treatment. During 2025, there were no tier 2 or tier 3 samples in Wales, with 49 positive samples in tier 1. This demonstrates that the current industry strategy for mitigating PFAS risks is working effectively to protect consumers.
Tier
Raw water tests
Treated water tests
Total
Tier 1
11,312
18,646
29,958
Tier 2
42
42
Tier 3
11,354
18,646
30,000
Table 13 – Total number of tests in Wales including all results less than limit of detection
The most prevalent species detected in raw and treated water during 2025 was perfluorobutanoic acid (PFBA), accounting for 34% of all positive sample results. The table below sets out the other parameters detected.
Parameter name
Tier 1
Tier 2
Tier 3
Total
PFBA
9
–
–
9
PFBS
5
–
–
5
PFOA
5
–
–
5
6:2 FTSA; 6:2 FTS
3
–
–
3
6:2 FTAB
2
–
–
2
11CL-PF3OUdS
1
–
–
1
EtFOSAA
1
–
–
1
FOSA
1
–
–
1
MeFOSAA
1
–
–
1
PFDA
1
–
–
1
PFDoDA
1
–
–
1
PFDS
1
–
–
1
PFecHS
1
–
–
1
PFHxA
1
–
–
1
PFOS
1
–
–
1
PFUnDA
1
–
–
1
PFUnDS
1
–
–
1
Total
36
–
–
36
Table 14 – Raw water data – number of tests per tier greater than the limit of detection (LOD)
The most prevalent species in raw and treated water during 2025 is PFBA with 34% of all positive sample results, the below table sets out all the other parameters detected.
Parameter name
Tier 1
Tier 2
Tier 3
Total
PFBA
16
–
–
16
PFBS
11
–
–
11
PFUnDA
4
–
–
4
PFDA
3
–
–
3
PFDS
3
–
–
3
EtFOSAA
2
–
–
2
PFOS
2
–
–
2
11CL-PF3OUdS
1
–
–
1
6:2 FTSA; 6:2 FTS
1
–
–
1
9Cl-F3ONS
1
–
–
1
PFDoDA
1
–
–
1
PFHxA
1
–
–
1
PFNS
1
–
–
1
PFOA
1
–
–
1
PFUnDS
1
–
–
1
Total
49
–
–
49
Table 15 – Treated water data – number of tests per tier greater than the limit of detection (LOD)
Audit programme
Company
Audit name
DWR
Bolton Hill WTW – raw water deterioration and process breakthrough
DWR
Retailers desktop
DWR
Retailers desktop – Welsh Water supplied – note separate to DWR itself
HDC
Retailers desktop
DWR
Bottled water stores
DWR
Llyswen WTW and Llanigon SRV
DWR
Disinfection Policy desktop
Table 16 – Audits undertaken in Wales in 2025
During 2025, the Drinking Water Inspectorate carried out a programme of targeted audits to provide assurance that drinking water supplied to consumers in Wales remained safe, reliable and well managed. These audits form part of the Inspectorate’s routine regulatory work and are designed to test how effectively water companies manage risks to drinking water quality, particularly where past incidents or emerging concerns have highlighted potential weaknesses.
The audits undertaken in 2025 provided a detailed and practical assessment of how drinking water quality is managed across treatment works, distribution systems, emergency arrangements and non-household supply chains. They identified evidence of good operational practice, including effective treatment performance, improved outcomes from targeted capital investment and a strong baseline understanding of regulatory responsibilities. However, the audits also highlighted recurring weaknesses that could affect resilience, particularly in relation to clarity of documentation, consistency of risk assessment, assurance of critical control measures, and the management of assets, hygiene and operational procedures under both routine and challenging conditions.
Taken together, these findings demonstrate that while systems are generally effective under normal operating conditions, further work is required to strengthen robustness, transparency and preparedness. The suggestions and recommendations made to companies in assessment letters focused on areas such as end-to-end testing of critical controls, formalisation of procedures and decision-making frameworks, enhanced monitoring and data use, and better coordination and training for incident response. By addressing these areas and embedding learning from both audits and operational events, companies can build greater resilience, maintain compliance under a wider range of conditions, and continue to protect public health and consumer confidence.
DWR Bolton Hill works
The Drinking Water Inspectorate’s technical audit of Bolton Hill works identified generally sound operational practices, with orderly record keeping, well-maintained control systems and core treatment processes, including coagulation, dissolved air flotation clarification, rapid gravity filtration and granular activated carbon adsorption, operating broadly effectively. The site uses an automated coagulant dose optimisation system linked to live UV254 data, supported by jar testing validation, while triple-validated pH monitoring provides resilience in chemical dosing control. Routine monitoring and escalation arrangements for raw water quality at both intake stations and site inlet were also identified as positive features supporting operational awareness.
However, the audit highlighted important weaknesses in critical control assurance that could undermine resilience to raw water deterioration and breakthrough events. Notably, end‑to‑end functional testing of alarms and shutdown systems was not routinely undertaken, with real-world events being relied upon as evidence of performance. This creates a risk that monitor or communication failures could go undetected. Similarly, limited SCADA visibility of individual instrument performance, such as only displaying averaged values in triple‑validated systems without deviation alarms, reduces operators’ ability to identify faults affecting key control points.
Several operational and asset-specific issues were also observed on site. For instance, saturated oil absorbent mats were found beneath a flocculator drive, highlighting the need for clearer spill response and food-grade oil assurance, while rapid gravity filter operation presented potential risks due to fast return‑to‑service rates and temporary turbidity alarm suppression, increasing the likelihood of undetected breakthrough. In addition, historic GAC management practices were shown to have resulted in low iodine numbers across multiple contactors in spent media, indicating reduced adsorptive capacity and the need for accelerated regeneration strategies. The company have since instituted a minimum iodine number target to provide additional assurance of ongoing GAC performance across their assets.
Shortcomings in sampling, hygiene, and asset condition were also identified. Operational sample taps were found in poor hygienic condition and lacked clear flushing instructions, while site observations included mole activity on treated water storage embankments (Figure 40), raising ingress risks. Other issues included potential backflow risks in GAC washwater systems due to the absence of an air gap, and reliance on operator judgement for key decisions such as pump recommissioning and raw water response actions, often without defined decision trees or standardised procedures.
Overall, although only one formal recommendation was made, requiring a risk-based programme of end-to-end functional testing of critical alarms, the audit identified multiple areas where operational discipline, process verification and risk management need to be strengthened. The findings indicate that, although the works is generally well operated, improved assurance of critical controls, clearer procedures and more robust monitoring and sampling arrangements are essential to ensure resilience against challenging raw water conditions and to maintain consistent compliance.
Figure 40 – Treated water storage embankment with evidence of mole activity
DWR bottled water storage and management
One of the audits undertaken in 2025 examined the management of bottled water stores at two sites, Dinas and Kinmel Park. Bottled water is a critical part of emergency arrangements, particularly during loss of supply events, and must be stored and managed in a way that protects its quality from the point it is received by the company to the point it is delivered to consumers.
The audit took place in July 2025 and was prompted by the Inspectorate’s planned audit programme, as well as by recent industry events that had highlighted weaknesses in alternative supply arrangements; all companies across the industry were audited. In particular, a significant loss of supply event earlier in the year had demonstrated the pressures placed on bottled water storage and distribution systems during emergencies. The audit therefore focused on how well these systems function under both normal and event conditions.
Inspectors found that some aspects of bottled water management were positive. Procedures for accepting and storing bottled water were broadly aligned with industry guidance, and there was evidence that the company was reviewing its arrangements in response to recent events. However, the audit also identified a number of areas where improvements were needed.
At the Dinas site, bottled water was found in a building that was officially out of service due to structural issues. Despite signage indicating that parts of the building were not in use, some bottled water stored there was later distributed for consumption. The Inspectorate considered this inappropriate, given the risk of contamination from damaged walls and the potential presence of vermin. The company was advised that any storage facility identified as posing a risk to water quality should be taken fully out of service until made safe and secure.
The audit also highlighted weaknesses in stock management and tracking. Inspectors found that batch numbers were not always recorded correctly and that information was sometimes shared informally, increasing the risk of errors. This made it difficult to trace bottled water once it had been moved between sites and would limit the company’s ability to respond effectively if a batch needed to be recalled. While plans were in place to introduce a more robust tracking system, the Inspectorate required updates on its implementation and stressed the importance of accurate records.
Further concerns were raised about how bottled water quality was assured on receipt from suppliers. Bottled water was not always sampled at the point it entered the company’s control, and certificates confirming compliance at the time of bottling were not routinely obtained. Although the company took steps to update its procedures following the audit, the Inspectorate emphasised that assurance should be in place before water is made available for distribution to consumers.
Overall, the audit concluded that while bottled water is an essential safeguard during emergencies, it should be treated with the same level of care and scrutiny as other parts of the drinking water supply system. The Inspectorate made several recommendations and required the company to demonstrate how it would strengthen storage conditions, tracking arrangements and risk assessment processes to ensure bottled water remains safe at all times.
Figure 41 – Bottled water stored within out of service area.
Figure 42 – Temporary storage of bottled water inside curtain sider lorry within the depot.
DWR disinfection policy
Disinfection is a fundamental barrier against harmful organisms in drinking water, and the policy sets out how treatment processes are designed, monitored and validated to protect public health. This audit was carried out as a desktop exercise during October and November 2025 and followed an earlier audit in which drinking water safety planning had been reviewed.
The purpose of the audit was to assess updates made to the disinfection policy and to determine whether it provided clear, reliable and evidence-based guidance for operational staff. Inspectors reviewed a range of documents covering treatment processes, performance targets and site-specific assessments.
The audit found that, while the policy addressed many relevant issues, there were significant areas where clarity and consistency were lacking. In several cases, the Inspectorate could not determine how key figures or targets had been derived, or whether they were supported by appropriate reference material. This included how treatment performance targets were set and how data was selected and analysed to demonstrate compliance.
Inspectors also identified concerns about how monitoring data was used. In some cases, data was assessed over rolling periods without clear definitions, which could allow poor performance to be obscured when older results dropped out of the assessment window. The Inspectorate considered this approach to pose a risk, as it could delay the identification of emerging problems and weaken the overall level of protection.
Another important issue related to how exceedances or failures would be managed. The policy did not always explain what actions should be taken if treatment performance fell below the required standard, or when such situations should be reported to the Inspectorate. Clear escalation and response arrangements are essential to ensure that risks are managed promptly and transparently.
The audit concluded that, although the company had invested effort in developing its disinfection policy, further work was required to ensure that it was fully robust, transparent and aligned with current scientific guidance. The Inspectorate made several recommendations and required the company to provide detailed responses and evidence to demonstrate how the policy would be strengthened.
DWR and HDC retailers
In Wales, the retail market differs from that in England, with non-household customers eligible to switch retail provider where their usage is greater than 50 million litres per annum. Although this reduces the number of properties in the customer base, these properties may present higher risk to the wider network because they are more likely to have complex plumbing systems or secondary private supplies. In Wales, two wholesalers and six retailers are involved in the supply of water to consumers. Across audits of non-household water quality and sufficiency management, findings indicated generally sound high-level arrangements and a good understanding of regulatory responsibilities among wholesalers and retailers.
However, several systemic gaps were identified that could affect resilience during water quality or supply incidents, including unclear and inconsistently documented roles and responsibilities, limited formalisation of communication arrangements, and insufficient recording and sharing of customer contacts and water quality intelligence. A key theme across the retailer audits was limited experience of water quality events and incidents, including escalation of urgent issues. This appeared to reflect limited opportunity, as relatively few occurrences have affected these consumers.
The absence of joint scenario-based emergency planning and training exercises was also noted, creating potential risks to preparedness and coordination during incidents. The audits also identified suggested improvements to staff training, particularly for frontline call handling, and limited mechanisms to track or escalate non-household customer issues.
Overall, while current arrangements appear adequate under normal conditions, the Inspectorate concluded that greater procedural clarity, proactive collaboration, and strengthened preparedness are needed to ensure robust protection of water quality and supply for non-household consumers.
DWR Llyswen works and Llanigon service reservoir completed capital scheme
The Drinking Water Inspectorate’s audit of Llyswen works and Llanigon service reservoir found that recent capital investment, including large-scale replacement of deteriorated iron mains, targeted network cleansing, and treatment process upgrades, has begun to deliver measurable improvements in water quality. These interventions have reduced the mobilisation of historic sediment, improved chlorine stability across the network, and contributed to a decline in discolouration contacts, supported by increases in residual chlorine observed at downstream booster locations and improved flow stability following installation of variable speed pumping.
Operational control and system resilience were generally assessed as effective, with good practice evident in areas such as pressure monitoring (figure 43) with clearly defined operating ranges, adaptive flow control to reduce surge impacts, and the management of supply during complex commissioning activities. Coagulation, clarification, and filtration processes were performing well under variable raw water conditions, demonstrating effective optimisation following earlier site upgrades.
Figure 43 – pressure monitoring
However, the audit identified several areas requiring further strengthening. Hygiene risks were observed in the storage and handling of temporary pumping equipment and pipework, while chemical management issues included insecure or damaged packaging and unclear containment arrangements for bulk deliveries, indicating potential contamination pathways (figure 44). Asset security and integrity also require improvement, with examples including non‑secure hatches, inadequate sealing arrangements, and insufficient perimeter protection, alongside risks associated with ancillary infrastructure such as unprotected air valves and nearby land use activities that could introduce contaminants.
Figure 44 – Torn bag of salt stored outside main works building
The new valve complex (figure 45), including air valves, at Llanigon service reservoir had been located on a throughway, used to move livestock between fields. This was also downhill from two large muck heaps, leading to risk of run off into the chambers. The Inspectors identified that damage to the concrete surround had already occurred, further increasing the risk. In response the company initiated regular inspections and recommendations were made to take steps to mitigate the risk, including removal of the muck heap, repairs to the concrete and covers and the frequency of inspection was reviewed for air valves at service reservoirs.
Figure 45 – Cracked air valve chamber at Llanigon service reservoir
The Inspectorate also highlighted the need for greater clarity and robustness in operational and investigative practices. Discolouration root cause analysis lacked sufficient evidential basis in some cases, with limited consideration of contributing parameters such as iron, manganese, and aluminium. Sampling arrangements and monitoring definitions were at times unclear, particularly during transitions in asset configuration, and there were gaps in demonstrating disinfection performance and contact time control during operational changes. These issues were compounded by a reliance on operational judgement in the absence of clearly defined procedures and consistent data interpretation.
Overall, the findings indicate clear progress following significant investment, but emphasise that sustained operational discipline, improved procedural clarity, and stronger asset and risk management controls are essential to secure and maintain these gains and to ensure consistent long‑term compliance.
Conclusion
The audits undertaken in 2025 provided valuable insight into how drinking water quality is protected across emergency arrangements and routine treatment processes. They highlighted good practice, but also showed that continued attention is needed to ensure systems, policies and documentation remain clear, consistent and effective. By addressing the recommendations made, water companies can strengthen public confidence and ensure that the safety of drinking water remains the highest priority.
Recommendations
Where a regulatory breach occurs or appears likely, and an Inspector cannot conclude that recurrence is unlikely, a formal recommendation must be issued to the company. Recommendations highlight areas where companies can improve compliance with the Regulations. Each recommendation is tracked to assess its significance and the company’s response. This regulatory approach helps identify companies at risk of regulatory failure that could increase residual risk to drinking water supplies, ensuring necessary improvements are made.
Inspectors made 89 recommendations in 2025, see table 17
High level category
Recommendations made
Management
62
Sampling
11
Storage & distribution
8
Communication
6
Treatment
2
Catchment
0
Other
0
Total
89
Table 17 – Category of recommendations made in 2025
Figure 46 – Number of recommendations per company in 2025
Figure 47 – Trend of recommendations in Wales
Figure 48 – Recommendation count national
As part of Dŵr Cymru Welsh Water’s transformation programme, thematic meetings continued to focus on key areas requiring measurable outcomes. One such theme is recommendations, which are particularly significant because the Recommendations Risk Index is one of the factors considered when assessing whether a company should enter transformation. The main aim of this thematic work is to support the company in improving its Recommendations Risk Index following three years of deteriorating performance. At these meetings, Inspectors discuss examples of responses to recommendations, illustrating the different response assessment scores available under the assessment procedure. Early lessons from these focused discussions included:
How to monitor the fulfilment of recommendations to the point of delivery with evidence.
What does delivery evidence look like? What is good quality evidence verses poor quality evidence?
How to determine the correct people to ‘own’ different types of recommendation.
The meetings are also an opportunity to discuss the fulfilment of current recommendations to help guide the company towards receiving a more favourable response assessment.
Although the number of recommendations issued to the company fell from 95 in 2024 to 83 in 2025, the company still received the second highest number of recommendations in the industry. This indicates that substantial further improvement is needed if the company is to move closer to average industry performance. One approach that has helped other companies on a similar journey is the early identification of potential recommendations during the investigation stage. Offering actions as part of investigation reports, where Inspectorate recommendations are assessed as likely, can result in the recommendation not being made.
Figure 49 shows that management deficiencies account for the largest share of recommendations, with 62 making up this portion. Sampling, storage and distribution and treatment deficiencies also attracted recommendations. Of the 62 recommendations in the management category, the majority were for risk assessment and policies and procedures.
Figure 49 – High level and secondary level categories
The Recommendations Risk Index shows the position of Dŵr Cymru Welsh Water and Hafren Dyfrdwy compared with the expected recommendation score for each company. Hafren Dyfrdwy is within the expected range, while Dŵr Cymru Welsh Water remains above the red line. This is expected given that the company remains closer to the start of its transformation journey than the end. Additionally, it takes a couple of years for the impact of recent years’ RRI to attenuate through the algorithm.
Figure 49 – Recommendation risk index
This year’s breakdown of recommendations by category reveals an increase related to consumer complaints during 2025, which correlates with the increase in complaints during the year.
Figure 50 – Recommendations per category in Wales
Enforcement
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. Table 18 summarises the total legal instruments served in 2025.
Type of legal instrument
Number
Companies
Regulation 27(4)* notice for improvements to water safety plans
1
Dŵr Cymru Welsh Water
Regulation 28(4)* notice relating to risks identified in water safety plans
1
Dŵr Cymru Welsh Water
Formally acknowledged improvement actions
1
Dŵr Cymru Welsh Water
Table 18: All enforcement legal instruments issued by the Inspectorate in Wales, in 2025 * The Water Supply (Water Quality) Regulations 2018
Details of enforcement action taken by the Inspectorate in the first half of 2025 was published in the interim report. Therefore, this report only contains details of enforcement served in the second half of 2025.
Enforcement served in Wales, in the second half of 2025
A notice was served on Dŵr Cymru Welsh Water under regulation 27(4) for improvements to its risk assessment methodology. An audit of the Drinking Water Safety Planning methodology and risk records identified deficiencies in meeting regulations 27 and 28. The notice requires updates to the methodology, including how risk assessments are undertaken and records are reported, to meet regulatory duties. These actions will be carried out alongside required updates following the issue of Information Letter 04/2025 on Drinking Water Safety Planning guidance. Following these changes, new risk assessments are to be provided to the Inspectorate by 21 October 2027.
One notice was served on Dŵr Cymru Welsh Water under regulation 28(4). Audits carried out at Felindre works and Llan y Mawddwy works identified deficiencies relating to disinfection. A similar notice was served in 2024 for works with off-site assets, such as contact mains extending beyond the site perimeter. As the deficiencies identified were not limited to the two works audited, a further company-wide notice was served to cover all works. This will improve disinfection management at 45 works, benefiting 2,238,526 consumers.
Enforcement Developments
In 2024, the Inspectorate reported that the milestone and closure reporting portal went live for drinking water quality legal instruments. In 2025, the portal was expanded to include a change application process and a facility to record the annual progress reporting. In future developments, the Inspectorate hopes to expand this facility to include NIS and SEMD legal instruments.
Transformation Programmes
Dŵr Cymru Welsh Water was placed into a transformation programme in June 2024, with five transformation notices issued from late 2024 to early 2025. The company is currently managing a total of 43 legal instruments across drinking water quality, NIS and SEMD, with two due for completion in 2026.
Since commencing this programme, the company has implemented a ‘Water Quality First’ initiative to reinforce the strategic importance of water quality across all operational areas.
Compared with other water companies at a similar point in their transformation journeys, Dŵr Cymru Welsh Water’s current position suggests that its transformation programme is more mature in structure, but that operational outcomes remain weaker and slower to improve. As with other large companies subject to enhanced regulatory oversight, such as Thames Water and Southern Water, Dŵr Cymru Welsh Water is managing a significant portfolio of enforcement activity and is seeking to strengthen governance, assurance and culture. However, it remains behind stronger-performing companies, such as United Utilities and Severn Trent, where sustained investment and more effective asset management have delivered lower compliance risk, fewer events and better consumer outcomes. Dŵr Cymru Welsh Water’s ongoing challenges with network discolouration, ageing assets and operational inconsistency mean it currently sits at the pressured end of the industry, even taking into consideration progress in governance and regulatory engagement.
Dŵr Cymru Welsh Water has made clear structural progress through its transformation activities “Water Quality First”, particularly in relation to governance, capability and regulatory engagement. This structure, established in year-one of transformation included dedicated leadership and new roles within dedicated teams, a governance framework and steering groups for decisions and direction, and formalised Key Performance Indicators (KPIs) being measured and reported through the governance framework. However, there is evidence of a loss of momentum in transformation leadership, most recently during 2026, following restructuring of the company with approximately 500 staff losses from across the business, including water quality teams. During the restructuring, assurances were provided by the company that front-line operations and transformation progress would not be impacted.
The improvements that have been made have not yet translated consistently into sustained operational performance, and material regulatory risk remains high. The key contributors to the company’s CRI score also remain unchanged, with network iron failures, coliform failures and taste and odour issues continuing to drive poor performance. When looking at events, particularly recovery and investigation, there are recurrent issues such as delayed escalation, inconsistent adherence to procedures, weak sampling strategies which results in poor evidence of water quality, understanding of the extent of the impact and compromised root -cause analysis.
The Inspectorate has communicated to the company that the following must be areas of focus, to achieve the water quality outcomes expected.
The delivery of long-term solutions rather than relying on short term management, particularly when inferior outcomes are achieved with the latter.
Re-focus of investment priorities, particularly risk of the supply of unfit water which is an offence, and the impact on customer experience.
An understanding of asset health, asset performance (including visibility) and asset suitability.
Consistent adherence to Governance processes and operational procedures.
Alternative supply arrangements
In summary:
The transformation programme is well established and strategically aligned.
There are signs of improvement in early indicators; but
The company is operationally reactive rather than consistently preventative.
Core water quality outcomes, asset resilience and compliance consistency remain below expected levels, requiring continued regulatory scrutiny.
The company has regular meetings with the Inspectorate’s liaison team, and six-monthly transformation meetings are held between the Inspectorate and notice sponsors within the company. During 2025, the company’s contribution to monthly meetings improved, and these forums are now used effectively to discuss notice direction, review progress and present information for early feedback before formal submission. This level of participation demonstrates a positive attitude towards the transformation programme. The company is encouraged to continue applying this proactive approach.
Despite overall progress, several setbacks occurred during 2025. Key milestones associated with legal instruments were missed, and the company did not notify the Inspectorate of delays until the milestone reporting deadlines. This reflects weaknesses in governance arrangements, oversight of legal instrument delivery and communication practices. This was particularly concerning given the frequency of legal instrument-focused meetings. The company has been reminded of the requirement to notify the Inspectorate at the earliest opportunity when risks to milestone delivery arise, and the Inspectorate has started to see improvement in this area.
The company’s successful completion of the service reservoirs and tanks notice was acknowledged in the Inspectorate’s 2024 annual report. This was under challenging conditions and was commendable. However, it has since become evident that prioritising this notice adversely affected progress on other legal instruments. In addition, a milestone within the same notice was identified during 2025 as not having been completed to the Inspectorate’s satisfaction. As a result, a subsequent regulation 28(4) notice was served in early 2026, to address deficiencies with sampling facilities.
A significant challenge for Dŵr Cymru Welsh Water is its discolouration performance, which is subject to a notice. The company did not achieve the AMP7 target in the notice. Biannual discolouration strategy meetings are now taking place between the company and the Inspectorate, and the company’s strategy is maturing. However, this has not yet translated into improvements in discolouration contact rates. It is not acceptable for consumers to receive drinking water with an objectionable colour, and the Inspectorate has imposed a stretching AMP8 target for discolouration improvement. The AMP7 target was 1.4 contacts per 1,000 population; the company achieved 1.8. The AMP8 target has been set at 0.7 contacts per 1,000 population by the end of the AMP period, which will require significant improvement. Progress towards this target will be monitored closely and the Inspectorate will consider further enforcement where improvements are not made.
Enforcement Performance Metric
During 2025, the Inspectorate developed and tested a new metric to measure company performance against obligations contained within legal instruments. The metric helps the Inspectorate direct enforcement resource to companies requiring the most attention and provides a transparent means of demonstrating company performance.
Every legal instrument served is scored, using a five-by-five matrix, which has a set of rules attached, which inspectors follow for consistency.
The first score, assigned when the legal instrument is created, is the seriousness score. This score reflects the origins of the legal instruments and ranges from voluntary programmes, through routine enforcement action, to escalated and transformation enforcement. The criteria are listed in table 19.
Seriousness
Score
Escalated enforcement – generally, enforcement orders but other forms too
5
Further (additional) enforcement – “child” legal instruments, transformation legal instruments
4
Routine enforcement (realised breaches) – such as compliance assessments, events, regulation 26 breaches, data driven, consumer complaints
3
Routine enforcement (potential breaches) – such as likely to breach, risk of breach, audit findings, risk assessments
2
Proactive schemes – such as AMP schemes, voluntary undertakings
1
Table 19 – Seriousness scores
The second score is a Red, Amber, Green (RAG) (expanded to include Amber + and Red +) status of the progress of the legal instrument. This score is assigned when the legal instrument is first created but is changed as required throughout its lifetime based on the progress of delivery. The criteria are listed below:
Red+ (5)
The Inspectorate has rejected a change application for date extensions to the completion date of the legal instrument.
Any delays that affect the end date of the legal instrument.
Once a notice is in Red+ status, it can only ever recover to Amber +.
Red (4)
The most recently submitted milestone is delayed or was delivered late.
The most recently submitted milestone is insufficiently evidenced or incomplete. This is where a report is rejected entirely, it does not apply for routine follow-up questions.
The Inspectorate has been notified that a future intermediate milestone is going to be delayed and there is no way the company can meet it.
The Inspectorate has rejected a change application for date extensions for intermediate milestones.
Last-minute notification of not going to meet targets, when clearly company have known for some time.
Missed completion report deadline.
Red applies until the next milestone is received, when the score may reduce to Amber or Amber +.
Amber+ (3)
Escalated enforcement (see table above) always begins at Amber+
New child legal instrument from a delayed legal instrument begins at Amber + (for example, an individual service reservoir (SR) being removed from a wider service reservoir notice).
Change application has been submitted and accepted, with a new final delivery date.
Legal instrument was previously at Red+ status, but company have resolved issues and improved management of notice.
Cannot go lower than Amber+ once here.
Amber (2)
Intermediate delay which does not affect the final date of legal instrument.
There have been delayed/late milestones, but scheme is now on track.
Previously red, but company have resolved the issues and improved the management of the legal instrument.
Cannot go lower than Amber once here.
Green (1)
Default option for all new legal instruments.
All milestones are on target or completed on time.
Change of solution which does not affect the final delivery date (ie the company have found a cheaper or quicker way of delivering the scheme within the notice period.)
The Inspectorate direct a future change to a scheme (for example, the publishing of new PFAS guidance, which affects PFAS undertakings)
The Inspectorate has initiated a change.
Small administration changes (such as an annex update to a discolouration notice).
Cannot return to green once amber or red.
The metric is calculated in a similar way to the Recommendations Risk Index. It recognises that risk will always exist and that larger companies, with larger catchments, more treatment works, more treated water storage, greater lengths of mains and more connections, will have higher residual risk. Total scores for each company are compared with those of the whole sector and normalised according to the proportion of the overall population supplied, producing an expected score for each company. Expected scores are then plotted against actual scores using linear regression. The upper 95% confidence value line is added to identify statistical outliers, producing Figure 51, the Enforcement Performance Metric for the end of 2025.
Figure 51 – Enforcement performance metric
During the first half of 2025, the Inspectorate applied a period of grace to companies for NIS and SEMD legal instruments, as the reporting processes and requirements were new to these areas. The Inspectorate sought to support, educate and advise, rather than reprimand, where items were delivered late or incomplete. While the Inspectorate will continue to provide advice on the metric, the period of grace has now ended and NIS and SEMD legal instruments will be scored appropriately. At present, there are only a small number of NIS and SEMD legal instruments compared with the total number of legal instruments. These are therefore included with drinking water quality enforcement in a single measure. This will be reviewed in future and they may be separated if there is benefit in doing so.
The metric shows that, as of 31 December 2025, no company operating in Wales was above the 95% confidence interval line. Dŵr Cymru Welsh Water has several transformation legal instruments, which carry high seriousness scores. The company will need to ensure timely delivery of these instruments to prevent increased RAG scores and the associated multiplication effect.
Security and Emergency Measures Direction – SEMD
2025 was the fourth reporting year for companies since the Inspectorate has regulated the Security and Emergency Measures Direction (the Direction). Companies have demonstrated an overall improvement in self-identification of the areas that they need to improve and move towards compliance of the Direction, resulting in significant investment in AMP8 over a range of schemes consisting of security and emergency planning improvements. This recognition has led to an overall decline in the reported Red, Amber, Green (RAG) position since 2022.
The Inspectorate undertook a program of on-site technical audits as well as event assessments and company interactions which resulted in a range of enforcement activity to secure improvement and compliance as demonstrated in Figure 52:
Figure 52 – SEMD Enforcement activity
Sufficiency
In September 2024, the National Infrastructure Commission (now NISTA) published a guide to Developing Resilience Standards in UK Infrastructure, identifying gaps in water industry regulation and recommending resilience standards for public water supplies. Key recommendations included: setting a peak demand standard for short-term supply capability; defining limits on consumers reliant on a single asset; and introducing forward-looking asset health metrics.
In response to the publication, the Inspectorate undertook analysis and research. The Inspectorate then drafted a report with proposed guidance on maintaining a sufficient water supply in response to the key recommendations identified in the NISTA report and incorporating the findings of independent research. The Inspectorate concluded that measurement of sufficiency serves as a practical indicator for both supply resilience and asset health.
Figure 53 – Key points for sufficiency
There was also a wider acknowledgement that no single lens would deliver the results that are intended in the NISTA report, so whilst sufficiency was the focus of the Inspectorates response it touches on a number of areas as shown in Figure 53. This work then allows other standards to be developed and work in conjunction with the sufficiency work.
The Inspectorate’s proposed guidance supports the principles of, clear definitions, risk assessment planning, collection of empirical data, measurable outcomes, exceedance conditions, event conditions, consumer validation and regulatory reporting. This is overlaid in a systems approach to identify and target areas that need investment the most. The Inspectorate will continue to work further with water companies and other relevant stakeholders including regulators to improve the development of sufficiency risk assessments and reporting pathways.
2025 RAG Summary for England and Wales
RAG (RED/AMBER/Green) Submission
The RAG assessment is a self-assessment tool used to report compliance with the Direction across 33 outcomes covering the full scope of SEMD.
Overview of RAG Movements
Since 2022, company red and amber self-classifications have increased, as expected in the initial years of assessment following regulator feedback from events and audits, and peer-to-peer benchmarking.
Figure 54 – Last 4 years RAG overview
Notable RAG outcomes in 2025 include:
Outcome 3.2: Alternative water – Most companies reported an Amber position for alternative water in 2025. Common weaknesses included insufficiently adjusted stockpiles, challenges deploying static tanks, and over‑reliance on mutual aid, which is not always available in practice. Events during the year demonstrated that alternative water provision can be constrained by location and accessibility rather than scale alone, and that supply chains are vulnerable during concurrent weather-related incidents. The Inspectorate reiterates that companies remain responsible for all customers off supply and must ensure plans are deployable under reasonable worst‑case scenarios.
Outcome 3.3: Vulnerable customers – This remains a persistent area of companies reporting non‑compliance within the RAG. During incidents, companies frequently apply an overly narrow definition of vulnerability and do not consistently prioritise all customers who meet the emergency planning guidance (EPG) definition. While some good practice was observed, companies must ensure that all vulnerable customers, including those beyond tiered priority models, receive appropriate support within required timescales and that prioritisation arrangements are clearly defined and evidenced.
Outcome 3.9: Communication – Although not always reflected in RAG self‑assessments, another area that has been noted by the Inspectorate as requiring improvement is communication during live incidents. The Inspectorate continues to identify significant shortcomings in incident communications. Events reviewed in 2025 show that customers often receive infrequent or vague updates, contributing to confusion and frustration. The Inspectorate reviewed an event where in the absence of updates from a company, social media rumours took over and people were queueing at bottled water stations that had not been announced, opened or even stocked. Companies are expected to provide timely, accurate updates during incidents, including minimum likely restoration times and clear information on alternative water provision, in line with EPG requirements for 24/7 accessibility and responsiveness.
Outcome 4.4: External suppliers – The majority of companies assessed this outcome as amber, reflecting limited visibility and assurance over extended supply chains, particularly subcontractors and overseas manufacturers. While contractual provisions are commonly in place, many companies report they lack effective mechanisms to test compliance in practice. Companies reporting stronger positions demonstrate clearer contractual expectations, routine reviews, and consistent application of security requirements across all suppliers and subcontractors.
Outcome 4.8: Personnel security – Requirements for role-based risk assessments have been in place since 1 March 2022, with guidance further reinforced following industry consultation in February 2024, and subsequently updated in protective security guidance (PSG). On 3 April 2024, the Inspectorate notified companies that audit evidence for personnel security procedures and measures would be required by 1 April 2025. Water companies have therefore received significant notice and time to advance their Personnel Security (PERSEC) measures.
Analysis by the Inspectorate indicated a trend among companies to shift from a Green rating to Amber or Red on the outcomes associated with the audit topic. Based on the companies’ self-assessments of this audit topic, 10 companies reported a deterioration in their RAG (Red-Amber-Green) positions. This pattern suggests that most companies are overestimating their compliance with the RAG guidance. The Inspectorate therefore issued an industry-wide recommendation for companies to undertake a rigorous and candid evaluation of their risk profiles as part of the RAG self-assessment process.
Analysis of audit evidence by the Inspectorate found that companies reporting a decline in outcome 4.8 have highlighted a range of vulnerabilities, including:
A shifting risk environment and evolving threat landscape.
Weak key controls, with risks linked to lost and non-returned keys.
Absence of sufficient mover checks for internal transitions into sensitive roles.
Limited documentation and reliance on ad hoc local procedures.
No formal aftercare policy for personnel security.
Backlog, incomplete or no role-based risk assessments.
Inadequate personnel security checks for contractors.
Notable Events – England & Wales
In 2025, companies reported a range of security events as well as several large loss of supply events. Reported events included break-ins at works and attempted cable theft, including at one critical national infrastructure site. Following the personnel security audit undertaken as part of the RAG process, several events were also reported concerning the management of personnel security and the handling of sensitive information.
One company experienced a series of loss of supply emergency planning events, which it attributed to hot weather. The Inspectorate expects companies to have plans in place to continue supplying water at all times. Paragraph 4(a) of the Direction requires that plans for water supply must be prepared on the basis that the company must continue to carry out all of its water supply functions.
Critical National Infrastructure fuel theft
This incident involved unauthorised access to a CNI site to steal fuel from alternative water supply tankers which in turn allowed access to parts of the treatment process, although no treatment interference took place.
The site’s perimeter and gates suffered no damage during the theft. In the days before the theft, the main gate’s combination padlock had been replaced due to wear and tear, but the same combination was retained. It was unclear from the Inspectorate’s assessment if the combination was known to the hostiles.
The company did not initially recognise this event as a serious incident because some operational assets were outside the inner boundary enclosure. Although internal escalation did occur, the company is updating its reporting processes.
Following the incident, the company undertook 24/7 guarding with strict access checks and regular patrols of both the perimeters and operational assets outside the inner fence. Longer‑term measures are now in place.
Serious organised crime
In January 2025, a water company reported a security incident at a CNI site involving attempted metal theft. Intruders accessed the site via adjacent farmland while the control room operator was undertaking site rounds. Although alarms were triggered, no access was gained.
Following the incident, the company implemented a range of mitigations. A perimeter fence upgrade was commissioned, and staff were briefed on intruder risks and escalation requirements. The Inspectorate determined that the seriousness of the event warranted a targeted audit of the site, which was undertaken on 19 March 2025.
Network and Information Systems – NIS
The Network and Information Systems Regulations 2018 ensure that the operational technology used to maintain the production of drinking water remains robust and operational. This supports the delivery of wholesome water at all times and without disruption. In England and Wales, implementation and operational delivery of the NIS Regulations is delegated to the Inspectorate. This is achieved by regulating and overseeing compliance with the NIS Regulations through assessment of cyber resilience and operational technology security.
Operational technology 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 by focusing on control of the physical environment rather than data processing and management. Operational technology controls the operation and automation of equipment used for abstraction, treatment and distribution of drinking water, including forwarding pumps, chemical dosing pumps, valves, water quality protection shutdown systems and automated safety systems. It is critical to the automated, safe and cost-efficient production of wholesome drinking water. To protect this essential service, these technologies must be suitable, secure and fit for purpose to ensure continuous, reliable production while defending against evolving threats to 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. Access to such technology by threat of actors with disruptive intent would have potentially serious consequences.
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 Inspectorate. 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 contributing outcomes of good cyber practice. This risk assessment informs investments plans and areas requiring additional controls.
Between 2023-2024, every water company was subject to an Inspectorate cyber resilience audit to verify each company’s self-assessed CAF assessment. Two companies were issued 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 Inspectorate enforcement.
During 2025, the final cyber resilience audit was completed. The Inspectorate also met with companies 62 times with nine in-person meetings. Desktop audits were conducted looking into progress made in 2025 against the 2024 audit. Companies were asked for evidence on Contributing Outcomes (COs) where they stated they had made a progress in 2025.
Materials in contact with drinking water (Regulation 31)
Regulation 31 prohibits a water company from applying any substance or product to water, or introducing any substance or product into water, where it may affect drinking water quality. This includes all chemicals, construction products and treatment products used by water undertakers, from the source of the water to the point of delivery to the consumer’s building. This is a critical duty because materials can affect taste or odour, or leach harmful substances into water. The regulation sets out how approvals may be given to construction and treatment products and materials that do not prejudice water quality or consumer safety.
During 2025, 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:
Figure 55 – Regulation 31 applications, changes and reapprovals
The Inspectorate has continued working with IT partners to further develop the regulation 31 portal for product approvals, which has been well received overall. The new system replaced manual application forms with online, interactive application forms that guide applicants in providing the information required for an approval, product change or reapproval to be considered. The online process supports accessibility standards, allows applicants to see the stage their applications have reached, and will make the process available to more users. The next phase of the project will deliver an end-to-end process.
In August 2025 we published a letter (DWI Ref: R31-06/2025) launching the new online interactive List of Approved Products. This has transformed from a monthly, published PDF document to an interactive, searchable website which is updated in real-time, something long requested by the industry and applicants. This has effectively become a live, online catalogue of approved products and can be found at: https://www.dwi.gov.uk/drinking-water-products/resources-for-water-companies/approved-considered-products/approved_products/.
Identification of poor product stewardship continued throughout 2025, with several approved products revoked from the Secretary of State’s List of Approved Products with immediate effect. All issues identified resulted from unauthorised changes being made to a product. Even small unauthorised changes to product formulation, material or components may create unacceptable changes to water quality or present a risk to public health. It is therefore essential that all changes to formulation are approved before products are supplied.
Where manufacturers have applied for changes to approved products, these will have been reviewed and where necessary testing undertaken prior to being accepted. This ensures that there are no issues with the products when in use.
The table below lists the products revoked and the associated letters issued during 2025 with some products completely revoked and requiring a full re-application and other products having conditions of use imposed.
Regarding Arlington 1000 Litre Bag-in-Box Combo Liner, conditions of use were applied to the product rather than a full revocation to allow water for domestic use to be available during the summer where many water companies were experiencing prolonged dry weather. This is an example of the pragmatic approach taken by the team during the year.
Date
Action
Product / Manufacturer
Reference number
Details / Conditions
Jan 25
Revocation of product approval
GF ABS Pressure Pipe / George Fischer
R31-01/2025
Jan 25
Revocation of product approval
8040-SBNF-DWI Membrane Elements / Mann+Hummel Water and Fluid Solutions
R31-02/2025
Apr 25
Revocation of product approval
PE100 High Performance Black Pipe / Radius Systems Ltd.
R31-03/2025
Aug 25
Update to requirements for approval
Arlington 1000 Litre Bag-in-Box Combo Liner
R31-04/2025
This product cannot be used for drinking or cooking purposes. Changes take effect from 06/08/2025.
Aug 25
Update to requirements for approval
Amazon SupaSpun II Cartridge Filters and Amazon SupaGard Cartridge Filters
R31-05/2025
Products supplied before 06/08/2025 shall be quarantined and cannot be installed. Stocks of already purchased product must be quarantined and clearly labelled as not to be used until further notice.
Table 20 – products revoked and the associated letters issued during 2025
Issues with some of the revoked products have since been resolved and these products have returned to the List of Approved Products. It should be noted that the name of the product and reference number are likely to have changed. Others will be undergoing full review and additional testing to verify whether they can be approved.
The Inspectorate does not take decisions to revoke products or prohibit their use lightly. However, where the stringent requirements for maintaining product approval are not met and there is a potential concern to public health, revocation may be necessary. Use of an unapproved product is an offence and may be prosecuted under regulation 33.
In addition, several approval holders either made late applications or omitted to apply for product reapprovals which resulted in a delay in reapprovals being assessed. This resulted in an increase in expired products with manufacturers having to undertake the entire process of product approval from the beginning.
In December 2025, manufacturers were informed via letter, DWI Ref: R31-10/2025, that there will be a requirement for all recognised grades currently contained in Annex 3 of the List of approved Products, to go through the approval process with the requirement that they apply for this approval by end of June 2026. This allows us to keep an updated list of recognised grade products and their current formulations.
There has been significant work undertaken by the Inspectorate to secure testing facilities for BS6920 and full regulation 31 testing throughout the year with five laboratories being added to the list of designated laboratories for BS6920 testing in February 2025. A laboratory was recently designated to undertake full regulation 31 testing capability, and we continue to work towards increasing this capacity throughout 2026. We are also collaborating with the water industry to resolve the issue, and this work continues. Laboratories are required to demonstrate and evidence compliance with the relevant standards to become designated for regulation 31 testing. Following members of the regulation 31 team presenting on the challenges of regulation 31 testing and discussion at Northumbrian Water’s Innovation Festival in July 2025, the team has also collaborated with Ofwat’s Innovation Enablers team to publish an Expression of Interest for progressing further laboratory testing which is due for publication in Q1 of 2026. This work seeks to provide a pathway for laboratories to undertake full regulation 31 testing requirements.
Research publications
Five research projects were published in 2025. A summary of each is included below.
Effectiveness of Water Treatment Processes in the removal of Endocrine Disrupting Compounds (EDCs)
This project concluded that endocrine disrupting chemicals were present in source waters supplying all three drinking water treatment works investigated, although concentrations were highly variable spatially and temporally. Most substances were not detected at concentrations above analytical limits of detection, indicating generally low prevalence. Where detections occurred, steroids and nonylphenol were consistently identified, aligning with historical monitoring data. A key conclusion was the identification of di-isobutyl phthalate in approximately half of all samples, representing the first quantitative evidence of its widespread presence in drinking water sources.
Due to the low frequency of positive detections and limited sample size, the study concluded that treatment removal efficacy could not be quantified with statistical confidence. Although DIBP removal appeared more consistent at the site employing slow sand filtration, this observation could not be robustly substantiated. Overall, the project concluded that existing monitoring approaches are insufficient to draw firm conclusions on treatment performance for EDCs. The absence of a health‑based guideline value for DIBP was identified as a significant regulatory gap, highlighting the need for further toxicological assessment and improved monitoring to better support future risk management
Bench-Scale and Pilot-Scale Water Treatment Efficacy Studies of PFAS Removal
This project concluded that the effectiveness of treatment processes for PFAS removal varies significantly depending on PFAS chain length, chemical structure and treatment technology. Adsorptive processes such as granular activated carbon and ion exchange were found to be effective for longer‑chain PFAS but consistently less effective for short‑chain compounds, with PFAS breakthrough early in testing. Ion exchange demonstrated greater capacity and longer operational performance than granular activated carbon, although both were influenced by source water quality.
Membrane processes, particularly nanofiltration and reverse osmosis, achieved the highest removal efficiencies, with reduction rates of up to 99% for many PFAS and greater than 80% for short-chain compounds. Nanofiltration was identified as preferable to reverse osmosis due to comparable removal performance at lower operating pressures. Advanced oxidation and reduction processes were generally ineffective at the doses tested, while coagulation achieved only modest removal. The study concluded that pilot-scale testing should focus on granular activated carbon, ion exchange, surface-modified clays and nanofiltration to determine their operational feasibility at full scale.
Organophosphorus Flame Retardants – Risk to Drinking Water in England and Wales – Phase 2
This project concluded that organophosphorus flame retardants are detectable in both raw and treated drinking waters in England and Wales, although concentrations are generally low. Tri(2‑ethylhexyl) phosphate was identified as the most frequently detected compound and was present at the highest concentrations across monitored sites. Removal efficacy varied substantially between substances and treatment works, indicating inconsistent performance of conventional treatment processes.
Human health risk assessment concluded that exposure to the monitored flame retardants via drinking water is unlikely to pose an appreciable risk to human health under current conditions. However, the study identified significant uncertainty regarding usage for flame retardants in the UK, which limits confidence in exposure assessments. The project concluded that improved data on use, catchment risk and targeted monitoring of the most frequently detected compounds would significantly enhance understanding of potential future risks to water supplies.
Disinfection technology and alternative disinfection for commercial water
This project confirmed that the most widely used disinfection technologies in England and Wales are UV treatment and sodium hypochlorite, reflecting their effectiveness and operational familiarity.
The analysis concluded that hypochlorite solution offers the most balanced overall disinfection performance, particularly in terms of microbial removal efficacy, cost and asset management, despite its potential to form disinfection by‑products. UV disinfection ranked second but was associated with operational complexity. Chloramination and ceramic candle filters were concluded to be unsuitable as standalone disinfectants. Assessment of international practice identified ultrafiltration, mixed oxidant solutions and peracetic acid as warranting further investigation, while bromine was identified as requiring caution due to uncertainties regarding by‑product formation and health impacts.
Cryptosporidium– Review of the reports of the group of experts, literature and events
A review of previous expert guidance, combined with analysis of Cryptosporidium events in England and Wales between 2005 and 2022, demonstrated that failures do not arise from a single dominant cause. Instead, events were most commonly associated with insufficient treatment in relation to catchment risk, failures or deficiencies in assets, and weaknesses in operational procedures or staff training.
The project further concluded that while regulatory frameworks and guidance have evolved, continued vigilance is required across the full water supply system, from catchment to consumer. A wide range of monitoring and detection options are now available, including surrogate measures such as turbidity and particle counting, as well as direct detection methods using oocyst counts and molecular techniques. Emerging detection technologies were identified as offering potential future benefits, although their role in routine regulatory monitoring requires further evaluation.
In terms of treatment, the review concluded that multiple effective barriers are available, including physical removal, ozonation and ultraviolet disinfection. Newer technologies, such as ballasted clarification and ceramic membranes, were identified as particularly promising based on recent large‑scale UK installations. Overall, the project concluded that effective Cryptosporidium control relies on a systems‑based approach integrating catchment management, resilient treatment design, robust asset maintenance and competent operational practice, supported by up‑to‑date evidence and stakeholder engagement.
Chief Inspector’s Expert Group – Governance framework for rainwater harvesting and greywater reuse systems
England and Wales are facing a real water scarcity challenge. The Environment Agency has predicted a demand gap of five billion litres per day by 2055 and tackling that requires action on multiple fronts, including making smarter use of the water we already have. In 2025, the Chief Inspector’s Expert Group produced this report: Governance Framework for Rainwater Harvesting and Greywater Reuse Systems. The report sets out how rainwater harvesting and greywater reuse (collecting water for uses such as toilet flushing, garden irrigation and laundry) can play an important role in reducing demand on our drinking water supply, whilst keeping public health firmly protected. Key findings include:
Up to 22% of household water use goes on toilet flushing alone – all of which could safely use harvested rainwater or greywater instead of drinking water.
Mandatory accreditation for water reuse installers and contractors (similar to the Gas Safe Register) would give the sector the credibility and consistency it needs to grow safely.
As the technical experts in drinking water safety, we are committed to building public confidence in water reuse and this report provides the evidence base to show it can be done safely and effectively.
Countries such as Germany and Belgium have safely practiced rainwater harvesting for over 20 years – there is a clear and well-trodden path for England and Wales to follow.
There are ten recommendations and the Inspectorate is working with others to take the work forward.
Whistleblowers
Ten disclosures were made to the Inspectorate during the reporting period 1 April 2025 to 31 March 2026. Of these, nine required further investigation by the Inspectorate. Further action was taken in response to five disclosures following investigation, including the issuing of recommendations relating to company processes, policies and procedures.
To help foster an open and supportive culture, the Inspectorate encourages companies to introduce reporting routes for water quality and network information systems concerns, similar to arrangements some companies have in place for health and safety concerns, and to maintain a formal whistleblowing policy.
Working with stakeholders
The Inspectorate updated and published its Vision and Strategic Objectives 2025–30, setting out priorities for the next period and into the integrated regulator. The Inspectorate works with a wide range of external organisations, regulators, government departments, professional bodies and academic institutions in delivering its strategic objectives. Specific updates on collaborative work carried out by the Inspectorate in 2025 are provided below.
Figure 38 Water Industry stakeholders
Figure 55 – DWI Stakeholder engagement map
Water Reform
The Inspectorate is closely engaged in work to reform the sector and create a unitary regulator. It has worked, and will continue to work, with Defra, Welsh Government, the Environment Agency, Natural Resources Wales, Natural England and Ofwat to deliver a reformed regulatory system that maintains public health protection at the core of drinking water supply regulation.
This aligns with the England report style by presenting reform activity in a neutral, factual and regulator-focused manner.
RAPID
This work sits alongside wider efforts to future-proof our water supplies. RAPID (Regulators’ Alliance for Progressing Infrastructure Development) has recently published a series of explainers on the four types of infrastructure needed to meet future demand – reservoirs, water transfers, recycling schemes, and desalination – which together with water reuse paint a picture of a resilient water future for England and Wales.
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.
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.
In 2025 the Inspectorate hosted the spring ENDWARE meeting on HMS Belfast in London and was joined by representatives from multiple countries.
Water Safe
The Inspectorate has a six-monthly liaison meeting with Water Safe and works collaboratively on campaigns. This year, we shared information about the illegal use of lead solder on drinking water supplies, and supported a publicity and education campaign for plumbers.
Tell us whether you accept cookies
We use cookies to collect information about how you use GOV.UK. We use this information to make the website work as well as possible and improve government services.
Cookie Consent
Cookies on dwi.gov.uk
Cookies are files saved on your phone, tablet or computer when you visit a website.
We use cookies to store information about how you use the dwi.gov.uk website, such as the pages you visit.
We use 3 types of cookie. You can choose which cookies you're happy for us to use.
Strictly necessary cookies
Always On
These essential cookies do things like remember your progress through a form.
They always need to be on.
Cookies that measure website use
We use Google Analytics to measure how you use the website so we can improve it based on user needs.
Google Analytics sets cookies that store anonymised information about:
how you got to the site
the pages you visit on dwi.gov.uk and how long you spend on each page
what you click on while you're visiting the site
Cookies that help with our communications and marketing
Some dwi.gov.uk pages may contain content from other sites, like YouTube or Flickr, which may set their own cookies. These sites are sometimes called ‘third party’ services. This tells us how many people are seeing the content and whether it’s useful.
In addition, if you share a link to a dwi.gov.uk page, the service you share it on (for example, Facebook) may set a cookie. We have no control over cookies set on other websites - you can turn them off, but not through us.
