January to June 2025 – Chief Inspectors interim report
Published 14:03:10 GMT 9 December 2025
Glossary
Company code with its associated company name
AFW | Affinity water
ALE | Albion Eco Ltd
ALB | Albion Water Ltd
ANH | Anglian Water services Ltd
BRL | Bristol Water Plc
CAM | Cambridge Water Company Plc
DWR | Dŵr Cymru Welsh Water
ESP | ESP Water Limited
HDC | Hafren Dyfrdwy
ICW | Icosa Water Ltd
IWN | Independent Water Networks
ISC | Isles of Scilly
LNW | Leep Networks Water
NES | Northumbrian, Essex and Suffolk Water
PRT | Portsmouth Water Plc
SES | SES Water
SVT | Severn Trent Water Ltd
SEW | South East Water Plc
SST | South Staffordshire Water Plc
SWB | South West and Bournemouth Water
SRN | Southern Water Services Ltd
TMS | Thames Water Utilities Ltd
UUT | United Utilities Water Plc
VWP | Veolia Water Projects
WSX | Wessex Water Services Ltd
Executive summary
The interim report for the first half of 2025 highlights several significant operational and compliance issues across water companies in England and Wales. Multiple microbiological detections were reported at treatment works operated by Southern Water, South East Water, and Bristol Water, with the Inspectorate generally concluding that operational processes were satisfactory but identifying potential weaknesses in sampling practices and infrastructure. Anglian Water faced regulatory scrutiny for failing to verify disinfection effectiveness at Gainsborough works, prompting recommendations for improved monitoring and validation arrangements.
Consumer complaints revealed systemic gaps in communication and escalation processes, with delays and mismanagement of water quality concerns underscoring the need for coordinated responses across company teams. In Wales, two notable events occurred: a “do not drink” restriction affecting eight properties due to backflow contamination from a toilet cistern, and a precautionary boil water notice following a private supply leak. Both incidents emphasized the importance of plumbing compliance and ingress risk assessments.
Several operational audits identified deficiencies in asset management and process control. At Bolton Hill works, inadequate functional testing of alarms and low iodine numbers in granular activated carbon pesticide removal processes led to recommendations for enhanced monitoring and accelerated media regeneration. Other events included discolouration complaints linked to inaccurate asset records and turbidity failures caused by lime build-up in treated water tanks, reinforcing the need for risk-based maintenance strategies.
Industry-wide lessons emerged from enforcement actions and technical audits, with the Inspectorate issuing 74 regulation 28(4) notices and two undertakings during the period. These notices primarily addressed overdue reservoir inspections, disinfection policy deficiencies, and microbiological compliance failures. Additional enforcement targeted identified risks from PFAS, requiring Wessex Water to install temporary treatment and accelerate long-term mitigation measures.
The report gives advice to companies that must strengthen risk management, improve consumer communication, and maintain robust operational controls to ensure regulatory compliance and protect public health. Recurring themes include the need for proactive asset maintenance, comprehensive monitoring of disinfection and chemical dosing processes, and effective contingency planning for water quality events.
Compliance and complaints
Microbiological detections at works
Southern Water – multiple treatment works
In February, Southern Water detected coliform bacteria in samples collected from the same day from three of its treatment works (Brede, Eastling and Sompting). The company undertook a thorough investigation into these detections, and it was identified that all of these breaches related to the same colony type (Klebsiella pneumonia) but were taken by separate samplers, from different regions of the company supply area. The investigations did not identify any risk associated with the operation of the water supply systems and all investigatory samples taken in response to this breach including swabs collected from the individual samplers’ cool boxes were satisfactory.
Whilst an audit completed at the laboratory did not identify any deficiencies within current working practices nor within the laboratory environment, further analysis completed on the colonies recovered from the samples indicated that contamination may have been introduced at some stage during the sampling activity or present in the sampling bottle or within the laboratory environment. Whilst the company completed a satisfactory investigation it could not definitively identify a root cause of the event.
South East Water – Newnham
In February, South East Water also detected coliform bacteria in a sample taken from its Newnham works in Kent. The site is a groundwater site which abstracts from a chalk aquifer. In response, the company conducted an investigation which confirmed that the works process was operating correctly with disinfection being maintained, and all investigatory samples taken from the site, reservoirs, and customer properties were satisfactory. The site investigation found a minor leak on the sample tap but this was not considered contributory to the failure. The contact tank at Newnham works, last inspected in 2009, is subject to a legal notice (SEW-2025-00019) requiring removal from supply for inspection by June 2026. In the interim, the company conducted an ROV survey and enhanced monitoring remains in place.
Bristol Water – Banwell
Bristol Water also detected coliform bacteria at its Banwell works in February. In response, the company conducted a satisfactory investigation which included a site inspection, a sampling survey, inspection of air valves and it brought forward the inspection of the treated water tanks. The company identified that five days prior to this breach, a leak had occurred on the strategic main system which can feed a treated water supply to Banwell works, however it was determined that due to the operation of this system at the time, this could not have contributed to the detection. The company did not definitively find a cause for this detection however, in response, Bristol Water has selected Banwell works as the first site for a new Hazard Review (HazRev) process, aimed at identifying and mitigating any risks across its sites.
Anglian Water – Gainsborough Reservoir Total coliforms March 2025
An initial site inspection was carried out on 11 March following the breach, with a subsequent inspection carried out on 12 March. No issues or ingress points were identified from the onsite checks of the treatment process. The internal condition of the upstream treated water tanks at Everton works and upstream storage point Gringley Reservoir 3 (Large) West were not believed to be a cause of the coliform detection. The treated water tanks for Gainsborough are due to be inspected, but the condition is currently unknown, so could not be ruled out as a potential cause of the coliform detection.Enhanced sampling was set up week commencing 17 March 2025 to continue until the treated water tank inspections had been completed. At Gainsborough works, it was noted that disinfection occurs by free chlorination through contact time (Ct) in the low lift sump. At minimum tank level and maximum flow, the Ct through the low-level sump is 1.72 minutes. The treated water is then pumped to the onsite Gainsborough Reservoir, which under normal system configuration also receives a supplementary flow of treated water from Everton works via Gringley Reservoir 3 (Large). The regulatory final water sample tap for Gainsborough works is located on the gravity supply to Gainsborough Low Level Distribution Zone, and therefore after the water has been blended.
The company’s response stated that disinfection at Gainsborough works was verified on site in accordance with the SSDP with appropriate alarm levels which automatically shut the site down to ensure the Ct is met at all times. From the information provided by the company, it was concluded that the company was not meeting the requirements of regulation 26(2)(b) and was unable to verify the effectiveness of the disinfection process at Gainsborough works. A recommendation was given for the company to review the disinfection process at this works and provide a solution to ensure that disinfection is verified at all times.
Industry-wide learning:
Disinfection verification should include appropriate monitoring, recording, and validation arrangements to demonstrate full regulatory compliance.
Complaints
United Utilities March 2025
A consumer contacted the company via an email sent to the company’s Environmental Information Office regarding their water quality concerns on 30 November 2024. The email was forwarded to the water quality and public health team on 4 December 2024, and the consumer was contacted by the company on 5 December 2024. However, there were delays in the initial company response because the request was made via a Freedom of Information request, instead of via the contact centre. The consumer also received poor communication with the company throughout their experience including; not receiving an email because it was sent to the wrong address, not receiving call backs from the company, the use of an incorrect name and date in an official correspondence to the consumer, miscommunication about the company’s complaints procedure, and mismanagement of requests for information.
Another consumer contacted the company via email on 25 February 2025 which included their full name and address and the water quality concerns the consumer was experiencing. It was noted that this email should have been escalated to the water quality team for investigation, however, the company only attempted to contact the consumer following receipt of the complaint investigation from the Inspectorate on 3 March 2025. The consumer’s complaint was not escalated to the water quality team for investigation, and this again highlighted a gap in company processes and procedures.
Recommendations were given to the company on these two occasions for the company to undertake a review into the different methods by which consumers can contact it and put in place measures to ensure that water quality concerns are highlighted, prioritised and escalated for investigation in a timely manner.
Companies need to ensure there is a coordinated approach across different teams to quickly and effectively address water quality concerns, and to ensure these contacts are appropriately handled, in a suitable time-frame and informative responses are provided.
Wales
Porth do not drink event
In May, Dŵr Cymru Welsh Water received a report from a consumer who said they had noticed a pink colour to their water supply. A company distribution inspector attended site the same evening to investigate and confirmed the presence of pink water at this property and a neighbouring property.
Image 1 – pink water coming out of a tap
Image 2 – pink water within a toilet cistern
A survey of the area identified eight properties on the same terrace who shared a common supply pipe and therefore a ‘do not drink’ restriction was given to all eight properties. A fast response by the company ensured these consumers were protected, given appropriate precautionary advice and provided with an alternative bottled water supply the same evening as the initial report from the consumer.
A water fittings inspection was carried out the next day which identified, in one of the properties, a flushing toilet cistern with a pink toilet block used within it. The water fittings inspector identified that the flushing cistern contained a float operated valve which did not provide the required air gap and therefore this was thought to be the cause of the problems observed.
One sample from the survey of the affected properties returned a result of three coliforms per 100mL. A resample collected later was satisfactory. Following rectification of the plumbing infringements and satisfactory samples, the properties were given the all-clear to use their water as normal.
Following the conclusion of the company’s investigation and actions, the company reviewed its handling of the event, to identify any learning. It was highlighted that the samples collected initially were not analysed for odour or taste as this was not in the associated procedure. Whilst samples collected from properties given ‘do not drink’ notices were understandably not tasted, an odour test, and taste and odour from up and down stream properties would have contributed to a suitable investigation. The company has subsequently reviewed and updated this procedure to ensure that odour and taste (where appropriate) analysis is undertaken for similar events.
Furthermore, a water fittings inspection at one of the affected properties identified a similar toilet cistern set-up to that of the original property, thought to have been the root cause of the event. Although there were no toilet blocks within the cistern, the pipework set-up meant it was highly likely that back siphonage could occur in the event of a depressurisation. An infringement notice was therefore also issued to this property, as well as the original property, to ensure backflow protection was in place. This event highlights the potential effects that common plumbing infringements can have on consumers and their neighbours.
Nantyglo Boil water notice event
An investigation into a private supply pipe leak on 21 January 2025 highlighted that the leaking pipework was located within a drainage chamber on the property. This was escalated to the Water Quality team and precautionary boil water advice was issued whilst further investigation and mitigation was undertaken.
All samples taken in response were satisfactory, the leak remained under positive pressure and was resolved with further samples taken before the advice was rescinded. The event highlights the need to assess potential ingress risks arising from supply pipe routing decisions across consumer properties, particularly where foul water drainage channels and chambers have been chosen by installers for convenience and/or cost-efficiency.
Bolton Hill Audit
An audit of raw water deterioration and process breakthrough was conducted at Bolton Hill works in West Wales in January 2025. The site was selected based on historic breakthrough of the taste and odour precursor 2- methyl isoborneol (MIB) with elevated concentrations in the wash water supernatant return playing a key role in the treatment challenge in May 2023.
Overall, the site was tidy and well run with evidence provided to demonstrate that company process control procedures were being followed. Raw water monitoring and alarm systems were in place for the discrete (remote) and combined sources.
Aids had been developed to inform operational responses to potential raw water contaminant breakthrough such as a local decision flow chart for Geosmin/MIB sample result responses relating to the control of the supernatant return and raw water systems. Of the 12 Granular Actived Carbon reactors (GACs) on site, 10 had spent carbon iodine numbers that were below 400 mg/g of carbon with the lowest at 257 mg/g of carbon. The company have since accelerated its GAC media regeneration programme for AMP8 to ensure that the new company iodine number target of 450 mg/g of carbon is achieved and sufficient GAC adsorbance capacity is maintained across its asset base.
An absence of routine functional testing was noted for some lower priority alarms on site, and a recommendation was made in relation to the enhancement of a risk-based programme of comprehensive, routine, end to end testing of all the critical site alarms and associated actions and controls to assure functionality and therefore compliance with regulation 26(4).
Companies are encouraged to perform regular functional tests of asset operational systems to validate the functionality of their designed control philosophies. Observations were made on the day of the audit that the individual readings of some of the dual and triple validated dosing system control monitors were not visible on SCADA and that monitor deviation alarms were also not displayed in some cases. Companies are encouraged to ensure that all parameters and associated functions used in the control of such systems are clearly displayed on site control systems.
Discolouration complaint 2025/1954
A water quality complaint was received by the Inspectorate in February 2025 in relation to ongoing discolouration being experienced by a consumer in Monmouth. Reactive samples taken at the property and immediate neighbours contained concentrations of iron above regulatory limits and on investigation an oversized 77m length of cast iron main directly feeding the properties was identified as the root cause. The material of this main was originally recorded on the company GIS system as MDPE but was found to be cast iron on investigation with records subsequently corrected. Accurate records are critical aids to investigations and companies are encouraged to focus on the robustness and feedback systems involved in maintaining this accuracy.
Flushing of this section of main was undertaken to remove accumulated sediment and it was then slip-lined to mitigate recurrence of the issue. During initial flushing activities follow-up sample results continued to fail for iron despite post flush colour grading being deemed satisfactory. Companies are encouraged to employ empirical flushing philosophies and practice to ensure the intended water quality outcomes are achieved and validated.
Events
Anglian Water – 23 January 2025 Winterton Holmes Works – Hardness Consumer contacts
Winterton Holmes works, situated in North Lincolnshire, is a ground water treatment works. On 27 August 2024. Winterton Holmes works was returned to supply following a period of five years and 17 days of being out of service for planned work. The company conducted sampling of the boreholes to meet the requirements of regulation 15.
Elsham works, also situated in North Lincolnshire, supplied both Winterton and Burton Upon Stath distribution zones whilst Winterton Holmes works was out of supply during the period July 2019 to August 2024.
From September to December 2024, the company received 65 consumer contacts for hardness or the change in water supply. The company notified the Inspectorate of this event on 23 January 2025 following the receipt of greater than 100 consumer complaints, enquiries or contacts relating to hardness or changes in the water supply.
The company’s investigation concluded that the final water pH of the water supply was 0.2 pH units higher than when in supply previously. The company used the Langelier Saturation Index (LSI) model to show the water had changed from fairly stable to likely depositing/precipitating when changed from the Elsham to Winterton Holmes supply. An LSI value >0.5 is considered to be scale forming and the company found the LSI at Winterton Holmes works in 2018 was previously 0.67. Between August 2024 and 23 January 2025, when phosphate was not being dosed at the works, the LSI value was higher at 0.83.
The company deemed it acceptable to return the works to supply without phosphate dosing, which is used for plumbosolvency control of lead service pipes. The phosphate dosing remained offline for five months whilst the site was in supply. This approach did not align with good practice for maintaining protection against lead leaching from the distribution network. A recommendation was made for the company to ensure that phosphate dosing is treated as a critical control measure when returning any works to supply where there is a known lead risk downstream. Following the reintroduction of phosphate dosing, the LSI decreased from 0.83 to 0.77, also demonstrating its positive impact on the final water.
It was also noted that the company has, on previous occasions, relied solely on its website to communicate important messages to consumers. A recommendation was made for the company to review all its risk assessments for hardness and where changes in supply will result in a change of perceived hardness and therefore acceptability by consumers, an appropriate and proactive method of communicating these changes should be used to reach all impacted consumers.
Lessons for the industry highlight the need for more proactive communication strategies that extend beyond passive channels, such as company websites. In circumstances where supply changes may influence water hardness or consumer acceptability, robust risk assessments and management plans should be i Implemented in accordance with Section 86 of the Water Industry Act 1991, requiring water companies to evidence their understanding of any water quality changes resulting from their actions and the mitigation measures proposed.
Yorkshire Water – 18 February 2025 – Barnsley Repeat Clostridium perfringens detections
A 2-inch cast iron main, in Barnsley, was excavated for a live burst repair on 10 February 2025. A further repair on 17 February 2025 required a shut off, which was completed by a Yorkshire Water employee. Flushing was not possible from a hydrant downstream of the repair, so the company requested that consumers at a property on the affected main flushed their taps for 20 minutes. Samples from the upstream hydrant and consumer property contained Clostridium perfringens.
Sampling continued on a daily basis until 27 February 2025, with Clostridium perfringens detections from numerous properties. Boil water advice was provided on 24 February 2025 and rescinded on 1 March 2025. The company acknowledged that the flushing undertaken at a consumer’s tap was inadequate to generate sufficient turnover of the main. Flushing from a consumer tap can also drag sediment into the smaller pipes of the property, causing blockages and damage. It was also clear that the company’s risk assessment did not adequately include details of how to proceed when an end hydrant is not accessible. A recommendation was given for the company to include clear instructions for ensuring appropriate flushing points are available or installed if necessary. The company acknowledged that an appropriate sample could have been taken after the repair from a downstream property, but the issue was not escalated.
The incident highlighted the importance of ensuring that flushing is carried out effectively from appropriate points on the network rather than from consumer taps. Companies should ensure robust processes are in place to assess and manage risks following repairs, including appropriate flushing, sampling, and escalation procedures.
Wessex Water – detection of sum of PFAS in tier 3
A sample collected by Wessex Water in February from its Charlton works located in Wiltshire was found to have a ‘sum of’ PFAS concentration of 0.103 µg/L which is within tier 3 in accordance with the Inspectorate’s PFAS guidance. The most likely source of the PFAS is thought to be from historical airbases and firefighting foams. Whilst the detection on its own is not an indication of worsening of risk (due to the historical nature of the land usage) the Inspectorate introduced updated guidance in August 2024 which now considers the combined concentration of the named 48 PFAS parameters, the ‘sum of’ PFAS. The inclusion of the ‘sum of’ PFAS as a precautionary guideline value has been agreed with UKHSA and is world-leading with England and Wales having one of the most comprehensive PFAS monitoring strategies globally, ensuring consumers can have complete confidence in the safety of their drinking water.
At Charlton works, the majority of the water supplied from the works undergoes blending with another source however a proportion of the water is supplied to consumers, potentially putting these consumers at risk.
The updated guidance requires the company to take action to reduce the concentration of PFAS to be low tier 3 in the short term and implement a longer-term strategy to progressively reduce the PFAS risk.
Wessex Water submitted a PR24 scheme for catchment investigation, design and installation of dedicated treatment for PFAS at its Charlton scheme which was supported by the Inspectorate and a regulation 28(4) was notice served to ensure the delivery of the new treatment. The delivery of the new treatment system was due by 2035, in accordance with the company’s risk reduction strategy as the site was previously demonstrating concentrations of individual PFAS in tier 2.
Following the tightening of the PFAS guidance and the detection of ‘the sum’ of PFAS in excess of the tier 3 guideline value, the Inspectorate took further enforcement action requiring Wessex Water to take short term action to reduce the concentration of PFAS in the proportion of the unblended flow whilst the new treatment works is being delivered. Wessex Water are installing temporary GAC treatment on the unblended flow, which is due to be delivered by the end of November 2025, and have brought forward the delivery of the new treatment works to the end of 2030. The Inspectorate revised its improvement notice to take into account the need to install the temporary treatment and to bring forward the milestone of the delivery of the longer-term solution. The Inspectorate, in its assessment of the event, also made some specific recommendations to Wessex Water around the frequency and laboratory turnaround times for monitoring PFAS at Charlton and the other sources used for blending and to ensure that there is a documented and verifiable blending plan for the proportion of the flow which undergoes blending.
Water companies are reminded to ensure that their PFAS monitoring and mitigation strategies are kept under continuous review and should any sites be exhibiting a change of risk, in particular for ‘sum of’ PFAS that they act quickly to ensure that short term mitigations can be deployed or installed to reduce the concentration to below tier 3, whilst the longer term mitigation is implemented. Where companies are using blending as a mitigation for PFAS reduction, companies should ensure that these are being effectively monitored and that the blending can be verified.
South West & Bournemouth Water final water turbidity events – Wendron, Dousland and DeLank works.
In March and April 2025 South West & Bournemouth Water reported three water quality events which resulted in high final water turbidity from three water treatment works: Wendron, Dousland and DeLank. Whilst the initial causative reason for the events at these works was different, the root cause for the elevated final turbidity leaving the works for each event was the same. The high turbidity was a result of lime build up in the final water tank combined with a change in flow or level in the tank. Two of the works are covered by legal instruments for cleaning an inspection of water storage tanks and the other works tank had been cleaned 10 years prior and was due for inspection and cleaning this year. One of the events also resulted in a prolonged loss of supply from the works.
The Inspectorate made a number of recommendations following these events including that the company review the frequency of cleaning of works tanks to reduce the risk from lime build-up resulting in elevated turbidity leaving the works, and to undertake measures to review and improve lime dosing and mixing at all sites which utilise lime dosing to minimise the build-up of lime in works tanks.
The Inspectorate reminds companies of the importance of using a risk-based approach to determine the appropriate frequency for the inspection and cleaning of water treatment works tanks, especially where chemical dosing may result in deposition within the tank. Also, that companies should either mitigate or have control measures in place to prevent the risk of lime build-up in works tanks to prevent a potential elevated turbidity event from a works.
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. A summary of the Legal Instruments issued in this quarter is below.
Type of legal instrument
Number
Companies
Regulation 28(4) Notice relating to risks identified in water safety plans
74
Anglian Water (23), Northumbrian Water (11), South East Water (31), Southern Water (2), South West Water (4), Thames Water (2) United Utilities (1)
Undertaking accepted under section 19(1) of the Water Industry Act 1991
2
Thames Water, Severn Trent water
Table 1 – Legal instruments issued in first half of 2025
There was a high level of enforcement activity in the first half of the year due to companies notifying the Inspectorate that they would be unable to fully deliver their legal instruments for tank inspections (and repairs where required). The inspectorate’s approach has been to separate tanks that exceed the notice dates into individual site notices. This is a moderate escalation of the enforcement, the alternative being to pursue section 18 enforcement orders. However, the Inspectorate takes water storage asset health seriously and since 2022, we have enforced where the time between asset inspections has exceeded 10 years.
Notices
Of the notices served, 58 of the 74 have been for tanks being removed from company-wide reservoir notices, as follows. Included in this number are those tanks where companies identified that specific engineering solutions would be required to remove the tank from supply. The companies and number of notices each are; Anglian Water (23), Northumbrian Water (3), South East Water (29), South West Water (3) and Southern Water (1).
Whilst it is accepted that some unanticipated delays will occur, particularly when unforeseen engineering challenges present themselves, the expectation is for this to be for 1 or 2 tanks per company. The high numbers of tanks that failed to be delivered within the notice timescale for South East Water and Anglian Water is concerning and possibly indicates wider project management issue, or that those companies have a higher risk appetite with respect to their treated water storage tanks. The Inspectorate shall continue to apply pressure to companies to assess and mitigate their risks associated with treated water storage assets, using enforcement where required.
A regulation 28(4) notice was served on South West Water for discolouration in its Trethurgy water supply zone. The company acknowledge that a 3 inch unlined cast iron main located within the zone is tuberculated and contributory to various consumer water quality complaints relating to discolouration received in; December 2020, October 2022 and September 2024. A regulation 28(4) notice was served to ensure the proposed filter changes, flushing, sampling and mains replacement scheme is delivered to the timescales outlined by the company.
Anglian Water have experienced exceedances of the Prescribed Concentration or Value (PCV) for Clostridium perfringens from samples of water leaving Welton works on five separate occasions in 2024 (February, twice in June, November and December). There has also been a coliform and an E. coli exceedance from Welton works in July 2023, followed by two further coliform detections in August and September 2023, breaching the requirements of regulation 4. The company’s investigations on site have been inadequate and have not satisfied the requirements of regulations 18 and 19, despite the elongated timeframe over which investigations could have been executed to determine a root cause. There is evidence that the performance of the rapid gravity filters cannot adequately show compliance with regulation 26 and the requirements of regulation 27. The notice requires additional, detailed investigation, which will include installation of additional monitors and a sampling programme for Clostridium and other microbiological parameters, to identify potential sources of contamination and the development of a mitigation plan. The company have opted to install ultraviolet treatment at the works. Under the notice, the company are due to deliver improvements before the end of 2025, protecting the wholesomeness of supplies to 50,306 consumers.
Following on from the Inspectorate’s technical audit of Northumbrian Water’s risk management of air valves, several deficiencies were identified, such as issues with the maintenance records, no risk-based inspection frequency, and the lack of clear procedures for all air valve inspections. The Inspectorate therefore served a regulation 28(4) notice upon the company to address the deficiencies identified. The notice covers all raw water impounding reservoirs, raw water mains, treatment works, strategic mains, service reservoirs and distribution mains in water supply zones within the company’s operating area and is due to be completed in March 2028.
A company-wide disinfection improvements notice has been served on Northumbrian Water due to many deficiencies identified during a technical audit of the company’s disinfection policy. In a rare occurrence for the drinking water sector in England and Wales, the company did not to return a completed draft notice or respond formally, following the receipt of a minded to enforce letter and so the notice was served entirely as written by the Inspectorate. The notice requires many factors to be reviewed and the disinfection policy to be updated once all are completed, ultimately ensuring that the disinfection arrangements operated by the company comply to its new standard. The notice is due to complete by the end of 2025 and effectively ensures wholesome supplies to all of the company’s consumers.
Five notices were served on Northumbrian Water for PR24/AMP8 schemes. These were schemes which had not originally been shared with the Inspectorate by the company. Ofwat identified, in its final reviews ahead of publishing its final determination in December 2024, that there were funded schemes with a drinking water quality impact, which the Inspectorate had not been sighted to. The company had initially submitted the schemes to Ofwat as resilience only schemes. On provision of the required information, the Inspectorate assessed there was a drinking water quality impact and supported the schemes. These were formalised as regulation 28(4) notices during the second quarter of 2025 and are summarised in the table below.
Conditional Allowance Schemes
The remaining three schemes were conditional allowance schemes. Thames Water agreed conditional allowances with Ofwat for specific improvements at Coppermills and Hampton water treatment works and at a third site. As with AMP schemes and in line with the principals of Better Regulation, the Inspectorate will track the progress of these schemes and provide feedback to Ofwat on their delivery. The specific schemes are detailed in the following table.
Affected site
Legal instrument type
Improvements being delivered
Affected population
Coppermills
Regulation 28(4) Notice
Improvements to the High Lift Pumping Station. Design, install and commission a slow sand filter recirculation system, allowing isolation of individual sand filters in case of disinfection failure. Design a permanent contact tank drain-down system.
2,784,147
Hampton
Regulation 28(4) Notice
Bulk recycle flow (pre-contact tank) to the Grand Junction Reservoir and upgrades to the emergency pumping facilities
4,699,778
Site 3*
Section 19(1) Undertaking
*This scheme falls under the remit of SEMD and so the details are not published in the public domain.
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Table 2 – Thames Water Conditional Allowance Schemes
AMP8 Schemes
During Ofwat’s final checks of its Final Determination, it identified several schemes which the Inspectorate had commended for support, but which were not being monitored by legal instruments or acknowledged actions. The Inspectorate therefore put in place acknowledged actions for these schemes.
Company
Scheme name
Details
Anglian Water
Bocking Taste and Odour
To remove chlorine dosing and instead install biological filters and UV disinfection, to mitigate taste and odour risks. The scheme will benefit 55,001 consumers and be delivered by 31 August 2029.
Anglian Water
Earls Colne Taste and Odour
For unchlorinated backwash water for filters. This improvement will remove taste and odour issues associated with site, due to biological filters affected by chlorinated back wash water. Installation to be completed by March 2030, benefitting 11,063 consumers.
Dŵr Cymru
Bontgoch filter refurbishment
First stage filter improvements to manage increasing raw water solids loading onto the site. This improvement will increase the backwashing capability of the first stage filters during periods of poor raw water quality, benefitting 28,876 consumers.
Southern Water
Disinfection Resilience
The original submission included 13 sites, 4 of these were included in R28(4) notices. The remaining nine were commended for support. A mixture of UV installation to protect against Cryptosporidium, hardening existing physical barriers or increasing contact time to enhance virus removal at the sites. Work to take place across AMP8 and be completed by 31 March 2030.
Table 3 – Acknowledged Actions for AMP8 schemes
Scheme name
Description
Barsham Nitrate
The company will install a nitrate treatment plant at Barsham WTW by 30 April 2032. This will protect the supply of wholesome drinking water to 116,040 consumers.
Langford Nitrate
The company will install a nitrate treatment plant at Langford WTW by 30 April 2032. This will protect the supply of wholesome drinking water to 367,960 consumers.
Langford Clarifiers
The company will complete clarifier improvements at Langford WTW by 30 April 2032. This will protect the supply of wholesome drinking water to 367,960 consumers.
Langford UV treatment
The company will install a UV treatment plant at Langford WTW by 30 June 2030. This will protect the supply of wholesome drinking water to 367,960 consumers.
Langham Nitrate
The company will install a nitrate treatment plant at Langham WTW by 30 April 2032. This will protect the supply of wholesome drinking water to 991,220 consumers.
Table 4 – AMP legal instruments served
South East Water were served with two additional reservoir inspection notices for Bloodshots reservoir 1 and Stanstead service reservoir. As with Anglian Water, the company have a company-wide notice requiring all reservoirs and other tanks to be inspected at a risk-based frequency, not exceeding 10-years. These two reservoirs have exceeded 10 years between inspections and are in addition to the 29 notices already served during the first quarter of 2025.
Similarly, Southern Water were unable to meet the dates in its company-wide reservoir notice for interstage assets at its Burham works due to interactions with site Final Enforcement Order (FEO), and requirements of enabling works with valves on site. The dates in the new notice, whilst a delay on the original requirements tie in with site shutdowns around FEO dates to enable more efficient project management.
The Inspectorate carried out an audit of United Utilities’ Sutton Hall works in November 2024, as a result of a significant taste and odour event. The Inspectorate identified shortcomings in the company’s management of the filtration and powdered activated carbon treatment stages. Consequently, to address the shortcomings, a notice was served upon the company to implement improvements. The notice will benefit 395,421 people and will be completed by September 2029.
The Inspectorate also varied a notice already served on United Utilities, during the quarter. Huntington water treatment works already had a notice in place, to implement a new start-up-to-waste project and other improvements. The Inspectorate carried out an audit of the works in December 2024, following on from a significant taste and odour event and a bacteriological compliance sample breach. During the audit, the Inspectorate identified shortcomings in the company’s Powdered Activated Carbon (PAC) dosing, filtration maintenance and management, and contact tank inspection philosophy. The Inspectorate therefore decided to vary the existing notice under regulation 28(6), to add further improvement requirements to the notice, to address the deficiencies noted. The improvements will benefit 1,679,511 people and will be completed in September 2029.
Undertakings
Severn Trent Water has given an undertaking to install telemetry upgrades on Boughton (Chester) works. The works is currently unable to store sufficient data from the onsite, electronic monitoring, where carried out for regulatory purposes. This is in contravention of regulation 34(1). All actions are due to be completed by the end of June 2027 and will help to ensure wholesome supplies to the 104,367 consumers supplied by this water treatment works.
Appendix – Compliance and events
Compliance
Parameter name
Reservoir
Supply point
Treatment works
Zone
Total
Aluminium
3
3
Bromate
1
1
Chloride
2
2
Clostridium perfringens
2
1
3
Coliform bacteria
149
149
E. coli
2
1
15
18
Enterococci
6
6
Fluoride
213
213
Gross alpha
15
8
23
Gross beta
3
3
Iron
56
56
Lead
25
25
Manganese
6
6
Nickel
28
28
Nitrite
1
1
Odour
27
27
Radon
6
6
Residual disinfectant – free
4
4
Residual disinfectant – total
5
5
Sodium
1
1
Taste
42
42
Total coliforms
31
27
58
Turbidity
7
4
11
Total
42
28
35
586
691
Table 5: Compliance failure summary – January to June 2025
Events
Company
Ongoing
0 (not an event)
1 (not significant)
2 (minor)
3 (significant)
Total
AFW
6
3
9
ANH
1
2
11
2
16
AWI
1
1
BRL
1
1
2
CAM
4
3
7
DWR
6
13
8
27
ICW
1
1
2
IWN
7
7
14
NES
1
1
PRT
2
1
3
SES
1
1
SEW
1
5
3
7
16
SRN
2
1
3
4
10
SST
4
4
1
9
SVT
14
11
5
30
SWB
5
5
4
14
TMS
15
9
7
31
UUT
2
1
3
4
10
WSX
3
2
5
YKS
3
9
3
2
17
Total
9
3
92
76
45
225
Table 6: Event summary – January to June 2025
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