Compliance, events and audits
Treatment works
Lartington works
Northumbrian Water had a turbidity breach at Lartington works in July. A regulatory sample taken from the works’ final sample point returned a turbidity of 1.1 NTU. The company attributed the turbidity result to deposits in the regulatory sample line which may have been dislodged at the time of sampling, as the sample tap upstand was found to be loose during the investigation into the detection. This was later rectified, and the sample tap upstand was fixed to a concrete pillar. The sample line from the outlet main was also rerouted. A turbidity exceedance of 1.3 NTU was previously reported in January 2024, which the company also attributed to sediment in the sample line. The sample line connection to the outlet main was replaced following the January exceedance. The Inspectorate gave two recommendations around the company’s auditing process which did not identify all the deficiencies with the sample point and to revisit the conclusions from the other audits, that the company had carried out at other treatment works, to ensure they were carried out appropriately. A suggestion was also given to review the weekly sample line flushing frequency.
Oswestry works
United Utilities had a coliform breach of 38 per100 ml in a sample from Oswestry works in August. On the days preceding the breach, significant valving operations were undertaken at Oswestry works to allow the installation of outlet pipework on the new second stage Rapid Gravity Filters (RGFs). In addition to valving, the work also necessitated diverting the entire works’ flow via stream 1, which involved closing the outlets on the stream 2 slow sand filters (SSF) and bringing them back online via stream 1. A defect was later identified with slow sand filter 12. The filter was removed from supply and an investigation revealed that a tile on the filter floor had moved out of place. This was subsequently rectified and returned to supply.
The company concluded that this could not be ruled out as the cause of the coliform detection. Further trends were provided in the exception report to demonstrate that the water had been adequately disinfected prior to and on the day of the exceedance. While the company were able demonstrate Ct was satisfactory on the day of the infringement, trends from the stream 1 UV reactors showed outages on the system. Follow-up information from the company confirmed that between May and October 2024 there were UV outages on 22 occasions at Oswestry works and Oswestry (at Hindford) works. It was concluded that the company had not complied with the requirements in the notice UUT-2022-00003 Oswestry, to complete the installation and commissioning of validated UV disinfection treatment capable of treating full works flow (180 ML/d) and to optimise existing treatment processes to ensure continuous compliance with regulation 26. An ‘intention to vary notice’ was served to the company.
The company have acknowledged the new requirement to report any outages of the UV system to the Inspectorate and are continuing to identify additional control measures that can be introduced to reduce the number or duration of outages of the system as well as reviewing the feasibility of installing auto changeover on UV1 and UV2 at Oswestry works (Hindford).
Whilst the company conducted a thorough investigation, it was unable to prove a root cause. The SSF defect may have been the cause, and thus highlighting the importance of multibarrier treatment. Whilst Ct was met, the UV barrier was demonstrated to be unreliable and therefore may not have provided its intended mitigation when it was needed.
Service Reservoirs
South East Water detected a single coliform in a sample collected from Chillies service reservoir number one in August. The service reservoir had recently been returned to service, having been removed from supply in September 2022 for internal remediation work and for work on local distribution pumps. During the investigation of this breach, it was established that the company did not sample the reservoir immediately before its return to service, instead a sample was collected two weeks prior however, in the meantime, the service reservoir had been drained and refilled. The Inspectorate recommended that the company collects service reservoir pre-commissioning samples from the actual volume of water that is going to be valved into supply, to confirm wholesomeness and that the company ensure lessons learnt from this breach were briefed to relevant teams.
Anglian Water detected coliforms in a sample collected from Etton service reservoir in July. Whilst the route cause was identified to be from ingress that was found on all nine technocover hatches, which was later rectified prior to returning the asset to supply, additional deficiencies were identified, as well as issues with other assets on the connected supply system. It was noted that the borehole CCTV surveys for the Etton and Northborough boreholes should have been conducted every AMP period and were overdue, with the previous inspections having been conducted between 1997 and 2008 for the four boreholes. It was also noted that there was no sampling tap on the incoming supply from Wing works, which made up approximately 50% of the supply at Etton service reservoir.
Recommendations were given for the company to prioritise CCTV surveys on the boreholes and as well as to install a sampling tap on the incoming treated water supply from Wing works, in order that future investigations can include appropriate sampling to rule out the quality of water from each incoming supply.
Zones
Following a taste and odour detection in Wessex Water’s Fovant zone in July, the company completed an investigation into the failure which included resampling from the original property and nearby properties. All follow up samples were clear and a review of consumer contacts from the area did not identify an increase in contact numbers. A water fittings inspection at the original property identified that there were rubber flexible hoses supplying the kitchen mixer tap and that the body of the tap remained warm. The company advised the consumer to replace both the tap and the flexible hoses.
The company investigation identified intermittent slight musty tastes from the upstream Fir Hill number 1 and 2 service reservoirs, so the Inspectorate recommended the company fully investigates these detections to ensure that there is not a wider issue with the water quality being supplied from these sites. The company had previously identified a risk with taste and odour due to inadequate turnover from these service reservoirs with the risk being under investigation in its regulatory risk assessments.
In August, Wessex Water had a breach of the taste parameter with the descriptor of ‘musty’ in a sample collected from a consumer property in the Danesborough zone. In the month prior to the breach, the company received above average numbers of taste and odour contacts from consumers in this water supply zone and had initiated an investigation. The company eventually identified the compound 2,4,6-trichloroanisole (TCA), which can cause a musty taste / odour, in post-contact tank samples taken from Durleigh works. The works was taken out of service in September and the Flexcrete Cementitious coating 851 lining in the contact tank, which had been applied in 2020, was found to be thin, eroding and peeling above the water line.
The company had previously experienced a similar issue at its Alton Pancras works in 2022, where the same coating had been used in the balance tank and TCA had subsequently formed. At Alton Pancras, the company removed the failed lining and applied a different liner. The company conducted a review identified that the product had also been used at a different site and initiated a sampling survey. Wessex Water is carrying out ongoing discussions with the manufacturer of the coating, the contractor and industry experts to establish the reason for the liner breaking down.
In September, United Utilities had a coliform failure in the Chorley zone. It was concluded that the company had conducted a satisfactory investigation, however, were unable to determine the cause of the exceedance. However, upon reviewing the trends that were provided by the company for the upstream works, an issue with the contact tank outlet and final chlorine monitors was noted from Hodder works where the company could not verify the effectiveness of disinfection. Two recommendations were given for the company to review guidance and training associated with its standard operating procedure and to review processes and training to ensure that the start-up to waste checklists are used and followed during a site start up.
Events
Lightshaw customer contacts
This event involved a planned change to the source water supplied to United Utilities consumers in areas of St Helens and Wigan in July 2023. Lightshaw works is located in Golborne, near Warrington. It treats ground water and is routinely brought into and out of service to balance supply and demand across the company’s supply system. When Lightshaw works is out of supply, the downstream water supply zones (WSZs) are supplied via water from the Rivington large diameter trunk main, a relatively softer water source. Lightshaw works supplies district metered areas (DMAs) within WSZs 120 (Lightshaw), 121 (Ashton) and 125 (Haydock).
Lightshaw works was returned to supply on 21 July 2023. One DMA that received a supply from Lightshaw works during this period was DMA 120-25, a relatively new DMA that was created between 2022 and 2023. DMA 120-25 was previously within WSZ 118 and had not recently received a harder water supply from Lightshaw works.
Between the 24 July and 6 September 2023, the company received 120 consumer contacts from WSZs 120 and 125, 49 of which were from DMA 120-25, expressing concern for water quality. The company also received a total of 366 written complaint letters from consumers also located in DMA 120-25. One consumer from DMA 120-25 contacted the Inspectorate to complain their water supply was discoloured and had made them ill. Due to complaints regarding water quality from consumers in DMA 120-25, the company rezoned the network in September 2023 to supply DMA 120-25 from WSZ 118 via the Manchester Ring Main.
Although the company carried out a risk assessment before returning Lightshaw works to supply, the risk assessment failed to adequately consider the effect of source water change on consumers, especially those who had not previously received a supply from Lightshaw works. The company did send proactive communications to consumers to inform them of a planned change to the water supply, however, the information provided failed to offer reassurance, and furthermore, several consumers did not receive any proactive communication from the company. The Inspectorate considers that the company failed to fully implement learning from the Copeland area event in 2017.
Sampling data provided by the company demonstrated that the water supplied to consumers during the event complied with the standards specified in schedule 1 of the Water Supply (Water Quality) Regulations 2016 (as amended). However, the Inspectorate concludes the company supplied unwholesome water when consumers were provided with water from Lightshaw works because it imparted a noticeable change to the appearance, taste and odour of the water supply, which consumers did not find acceptable. This is also evidence from the consumer questionnaires and statements that consumers rejected the water for drinking, cooking, and washing.
The company was issued a warning letter on 4 July 2024. The event highlights the importance of comprehensive risk assessments and effective consumer communication when altering source water supplies. Companies are reminded of their duty under section 68(1)(b) of the Water Industry Act 1991 where, so far as reasonably practical, there is no deterioration in the quality of the water which is supplied from time to time from a source or combination of sources. This also underscores the need for better anticipation of consumer acceptability issues, targeted communications, and more robust implementation of lessons learned from past incidents.
Following the event, the company commissioned independent research to review the contact data in the hotspot areas, previous communications and identify control locations for the research to understand the drivers for consumer contacts and to test behavioural science levers to determine effectiveness. As a result, the company communications were amended based on customer feedback and focus groups were reconvened to capture feedback following the redesign. The company found that the communication needed to set expectations effectively, neurodiversity and those with medical conditions should be considered and the revised communication provided more reassurance and covered customers key questions.
Yorkshire Water Oughtershaw service reservoir
A compliance sample taken from Oughtershaw service reservoir 24 September 2024 was found to contain 122 coliforms per 100 ml. On 25 September 2024, a restriction of use boil water advice was provided to one property downstream of the asset in the K848 Oughtershaw DMA and on 26 September 2024 boil water advice was provided to the remaining eight properties. An operational sample taken 26 September 2024 from Oughtershaw reservoir outlet, contain E. coli >1000 per 100ml.
A compliance sample from Oughtershaw service reservoir taken on 30 September 2024 contained 48 coliforms and 23 E. coli per 100ml. Compliance samples collected between October and November breached the standard for coliforms a further four times (see table 1 below).
| Oughtershaw service reservoir | Number of Coliforms / 100 ml |
|---|---|
| 16/10/2024 | 74 |
| 24/10/2024 | 3 |
| 01/11/2024 | 8 |
| 20/11/2024 | 43 |
Oughtershaw service reservoir was not fully bypassed and taken out of service until 4 March 2025. Microbiological water quality improved significantly thereafter, and the health protection advice was lifted at all properties on 13 March 2025. Restriction of use advice remained in place for consumers for 201 days.
The company carried out Cryptosporidium tests of 46 samples in total with no oocysts detected during the event. The Inspectorate noted a significant delay in the company’s investigation to the breach in September and the failure of the company to carry out a walk over of the main until 9 December 2024 where an unmapped air valve was discovered. In addition, there were still unanswered questions regarding potential cross connections with the old, decommissioned works onsite. A recommendation was given for the company to review its procedures to ensure that investigations are carried out in a timely manner to mitigate against further breaches.
The company state it is also in the process of creating a new continuous improvement team within the Water Quality department that will run root cause analysis reviews for all water quality events in future to prevent a recurrence.
The key learnings from this water quality event are critical and wide-ranging, particularly for improving operational response. Timely, thorough investigations and up-to-date asset records are essential for effective incident management.
Audits
Throughout the second half of the year, the Inspectorate carried out technical audits across the industry to evaluate works’ performance.
In October, the Inspectorate visited Southern Water’s Brede works and made several recommendations. Brede works is a surface water site treating water from Powdermill and Darwell surface water reservoirs and four interconnected wells. These were for the company to investigate and implement methods to ensure coagulant dose and DAF performance is optimised; to rectify the shortfall in media replacement which had not been corrected for six years; to investigate the settlement time following filter backwash which was recorded by the company to be 10 minutes long; to investigate the cause of the recurrent Clostridium perfringens detections and to develop robust short and long-term solutions to reduce the risk of further detections. Further recommendations were made against filter performance, operation, inspections, primary filter roof repair and planned maintenance to clean the filter lauders. In the long term, the Inspectorate recommended replacement of the filters with a more appropriate and robust solution.
The Inspectorate found the works’ final water turbidity alarm allowed water to enter the final stage of disinfection for 30 seconds at a turbidity greater than 1 NTU before allowing the works to shut down. A recommendation was made to the company to introduce an appropriate alarm to allow works shutdown before the requirements of regulation 26 are breached at this site. The Inspectorate reminds all companies that water with a turbidity of greater than 1 NTU entering the final point of disinfection is in breach of the Regulations and all precautions must be taken to prevent this scenario. Brede works is currently subject to an improvement notice, however the Inspectorate was minded to initiate further enforcement action following the audit.
In October, the Inspectorate also visited South East Water’s Green works. The works is a surface water Hazards Green works in East Sussex. Water is abstracted from the Wallers Haven River, Darwell Reservoir (which is managed by Southern Water) and an onsite well. South East Water list ‘media depth checks’ for filters as a control measure on the company regulatory risk assessment however at Hazards Green it was apparent these checks were not taking place. The Inspectorate recommended the company review all sites to ensure that media depth checks are being completed at the required frequency and that the company update its Drinking Water Safety Plans to reflect the work it has identified to improve the control monitoring systems at the site.
In November, the Inspectorate carried out an audit at Anglian Water’s Pitsford works, which is a large surface water site located in Northampton, supplied by the River Nene, Pitsford Reservoir and Holcot, Walgrave and Scaldwell Brooks. The most significant challenge at the works is from pesticides, for which there is Granular Activated Carbon (GAC) treatment in place.
During the audit, Rapid Gravity Filter (RGF) 1 and 8, were found to be drained down and out of service for filter nozzle replacement. A subsequent data request following the audit found that RGF1 had been out of supply since April 2021 and RGF8 since May 2022 as the company had not been able to procure approved nozzles. The Inspectorate was critical that the status of the remaining six filters was being impacted by the company’s passivity in addressing the refurbishment issue and it was recommended that the company remediate the filter issues on site as a priority, so that the requirements of regulation 4 are not impacted in future.
A further recommendation was made to review how the company’s maintenance systems highlighted instrument calibration dates in response to a turbidity instrument not receiving a timely two-year full loop calibration over a four year period between 2020 and 2024.
The Inspectorate also audited Affinity Water’s Kingsdown works and found the company has not reported any compliance data for the pesticides aldrin, dieldrin, heptachlor and heptachlor epoxide in recent years. A recommendation was provided for the company to ensure compliance with regulation 6 in regard to the four aforementioned pesticides at this works and across the company’s estate. Another recommendation was made to ensure samples from Kingsdown works are always representative of water leaving the works as required by regulation 16, since the final water sampling tap had the possibility of being supplied by the network rather than the works, if the works is not pumping in to supply.
Many further recommendations were made including to consider sewer pumping stations within the catchment risk assessment; to review the regulation 27 records for risks associated with generators and transformers to be considered and updates to the regulation 28 report made; to ensure risks associated with chlorate are controlled; and to hygienically seal an observation borehole located in close proximity to the site operational borehole.
The Inspectorate’s risk-based audit programme at works has found many recurrent themes across the industry, particularly with regards to inadequate filter performance and maintenance, site-wide risk assessments and general site maintenance. Optimal filter performance and filtration are critical components of the production of a safe and high-quality water into supply. However, at the majority of the sites audited, filter performance was found to be sub-optimal, with deficiencies observed in routine maintenance, inspection, cleaning and timely remedial interventions. Continuous risk assessment of treatment works should inform timely updates to regulation 27 risk assessments and 28 reports with appropriate short-, medium- and long-term mitigation and control measures in place. However, this was also found to be inadequate at some of the works that had been audited. Site maintenance was also overlooked at almost all the works audited, in some cases for years, leaving assets to deteriorate. The Inspectorate will always recommend or initiate enforcement to ensure compliance against regulation 4 in order to maintain wholesome water supplies to the public.