- Drinking Water 2024 – Summary of the Chief Inspector’s report for drinking water in England
- Foreword
- Water supplies and testing
- Compliance with water quality standards
- Water quality events
- Asset health and service reservoir integrity
- Consumer contacts
- Water safety planning and risk assessment
- Perfluoroalkyl and polyfluoroalkyl substances (PFAS)
- Audit programme completed by the Inspectorate
- Enforcement, transformation and recommendations
- Lead in water
- Materials in contact with drinking water (Regulation 31)
- Security and Emergencies (SEMD)
- Network Information systems (NIS)
- Research publications
- Raw water data
- Whistleblowers
- Working with stakeholders
- Annex A – Number of tests carried out by companies
- Annex B – Compliance with standards
- Annex C – Compliance failures and events
Water quality events
Water companies are required to notify the Inspectorate of any event which, by its nature has, or is likely to, adversely affect the quality or sufficiency of the water supplied to consumers. A notifiable event can also be any incident or occurrence that has caused, or is likely to cause, concern to persons to whom water is supplied. This is an intentionally broad definition to ensure that any occurrence in the water supply is quickly notified to the Inspectorate and that effective remedial action is taken.
In 2024, the Inspectorate was notified of 556 events in England. This is a 4% increase in the number of events reported in 2023 (533 events). The DWI adopts a fair and transparent approach to enforcement and will take action in accordance with the DWI’s enforcement policy in response to event assessments after careful assessment of the facts and circumstances of each incident by the assessing Inspector.
Figure 8 and table 14 – number of reported events per year
The diagram below illustrates the type of the events reported to the Inspectorate in 2024 and their impact on the water supply from source to tap. Some reportable events may have been outside of the company’s control. For instance, over 31% of reported events occurred on consumer premises and were attributed to pipework fittings, cross-connections, materials causing taste and odours, lead pipes, leaching of nickel contained within taps and connectors, improper use or absence of backflow protection and plumbing.
A further 12% of events were due to ground contamination, such as spillages of petrol or other chemicals transcending pipes, and nearly 12% were due to damage by third parties, such as roadworks damage by another company, media interest, vandalism, and other miscellaneous situations where the company has little or no control over. Therefore, approximately 55% of all water quality events reported to the Inspectorate were outside of the control of the water company. The remaining 45%, would have been within the company’s control.
Figure 9 and table 15 – 2024 events in England
The Inspectorate has developed a series of risk indices to identify where companies should address water quality risks to supplies. For events, the DWI use the Event Risk Index (ERI), which measures the impact of any events and the potential consequence on consumers as well as understanding the actions taken by the company in response. The ERI is designed primarily for the purposes of effective regulation, ensuring appropriate scrutiny is directed to those areas of greatest relative risk. The ERI is not a statutory measure, it does not remove the duty for a company to notify, investigate and respond to every event as set out in the regulations. However, as a risk-based metric, the objective is to incentivise the company to allocate its resources towards highest risk in a precautionary manner.
Figure 10 and table 16 – ERI since 2020, this is a sum of the raw score divided by the total population of each company
Event risk index by company
The ERI identifies companies who require additional regulatory mitigation measures to minimise any further impacts on consumers. The bar chart below shows the relative risk ranking of companies. Four companies; South Staffordshire Water, United Utilities, SES water and The Isles of Scilly are above the industry ERI. For the 2025 reporting year the Isles of Scilly will be incorporated into their parent company South West Waters reporting.
Figure 11 and table 17 – ERI by company for 2024
Highest Event Risk Index (ERI) scoring events
In determining the highest risks, ERI identifies those sites which present the greatest need for intervention by way of risk mitigation. The focus is on asset health because of the link to ongoing poor performance manifesting as repeated and ongoing failures to a larger proportion of consumers. Consequently, most of the 556 events notified to the Inspectorate in 2024 were of relatively short duration, and companies took appropriate action to inform and safeguard consumers and liaised with other stakeholders, the risk scores were low.
Figure 12 and table 18 – Top 10 ERI scoring events
Specific events
Elevated chlorate – Tresco and Buzza service reservoir (St Marys), Isles of Scilly April 2024
Chlorate and chlorite are disinfection by-products that can arise from the manufacturing process, or as degradation products, from the use of sodium hypochlorite, calcium hypochlorite or chlorine dioxide for disinfection or oxidation processes within drinking water treatment and supply systems. Concentrations should be maintained as low as reasonably practical without compromising disinfection. In 2017, the World Health Organization (WHO) Guidelines for drinking-water quality retained the provisional guideline value of 0.7 mg/l for chlorate and 0.7 mg/l for chlorite
As sodium hypochlorite solutions age or temperature increases, the amount of chlorate increases and the amount of available chlorine for chlorination / disinfection decreases. This makes it necessary to increase the volume of sodium hypochlorite solution dosed to achieve the correct level of chlorine which in turn increases the amount of chlorate in supply. At a time where climate change is likely to increase environmental temperatures, this risk is of increasing importance and has been highlighted in previous audits and reports to the industry.
In 2023, the Inspectorate undertook a chlorate audit of South West and Bournemouth Water, which included the Isles of Scilly. As part of the audit findings the company were requested to report (including retrospectively) any breaches of the 700 µg/L chlorate threshold as an event. The company reported two events for the Isles of Scilly in 2024 – Tresco and Buzza service reservoirs.
On the island of Tresco the water supply system comprises of a works and several service reservoirs. South West and Bournemouth Water have undertaken chlorate sampling at the works and the service reservoirs on Tresco since April 2021. Between 2021 and March 2024 a significant proportion of chlorate results from the works and service reservoirs on the island were noted to be > 700 µg/L. The chlorine control system at the works is a legacy system and dosing is via a recirculation system between the two tanks at the works. Sodium hypochlorite dosing pumps were at the time the event reportedly linked directly to a 25-litre drum. The dose was controlled via a chlorine monitor located on one of the tanks.
Buzza reservoir is located on the island on St Marys. Again, the company has undertaken chlorate sampling on the island since April 2021. Two samples taken from the reservoir exceeded 700 µg/L for chlorate in 2022 and 2024. The chlorine dosing system at the suppling works comprised a single 200 litre day tank, and a set of duty / standby dosing pumps. The day tank at the time of the event was filled by decanting 25 litre drums of sodium hypochlorite into the tank.
Following a previous audit in 2021 the Inspectorate made a recommendation to the company regarding the risk of the formation of degradation products (including chlorate) due to the chlorine storage, batching and dosing arrangement on the islands. The company in response amended their procurement arrangements of sodium hypochlorite and reduced the volume of sodium hypochlorite being ordered from 1000 litre bulk tanks and 200 litre bulk product to 25 litre drums.
In 2023, the company improved their stock rotation and sourced a supplier of lower strength sodium hypochlorite and commenced using the lower strength sodium hypochlorite in 2024 after modifying the dosing control at both works. The company furthermore reduced the number of sodium hypochlorite drums ordered, increasing the order frequency and reducing the storage time of sodium hypochlorite on the islands. In addition, the company applied a new internal trigger value for chlorate of 250 µg/L to initiate an investigation. In addition, following the audit the company produced site specific chlorate policies for the islands.
While the company were responding to the increasing challenge of chlorate formation it is necessary to improve further the management of the company’s sodium hypochlorite stock levels on the islands and the response to elevated chlorate results especially those which led to prolonged elevated chlorate levels.
The Inspectorate has served notices for Tresco Water Quality Improvements and St Marys Water Quality Improvements to ensure the company mitigates the known risks.
Precautionary boil advice – Coliform detections – Bryher, Isles of Scilly October 2024
In October 2024, compliance samples taken from the works and service reservoir on the island of Bryher by South West and Bournemouth Water contained a single coliform. The detection of a coliform in a service reservoir whilst not necessarily harmful, may indicate a defect in the asset and a potential risk. This report has highlighted the need to act on any such failure to identify the root cause. Rightly, the company undertook a sampling survey as part of the investigation and detected coliforms at another service reservoir and at consumer properties. In response the company issued a boil water notice was issued for the island to protect public health. Again, this is an appropriate approach.
In response to the coliform detections, the compartment of the reservoir was drained. . The company found a small dead bird near the outlet of the compartment. The inspection identified a small dead bird near the outlet as a result of the gauze protection missing from an air vent.
The company continued sampling, after issuing the boil water notice and E. coli was detected at one of the service reservoirs and at consumer properties reinforcing the validity of the precautionary step to advise water to be boiled.
The reservoirs had previously been inspected in 2021 by a third party and no inspection records had been completed. This serves as a reminder that inspections must have all records in order, especially those which are carried out by third parties to ensure work is completed to the expected standard.
A Notice was served for Bryher water quality improvements which includes coliforms and E. coli.
Southern Water – Testwood plant failure & loss of supply December 2024
When work is being carried out at a water treatment works which is in operation to maintain supply, this makes any intervention particularly difficult and not without risk. The complexity and extent of work ongoing at Testwood WTW by Southern Water certainly fits into this category. Nevertheless, it is appropriate that the company undertakes much needed work to improve the site.
In December 2024, Testwood works was shut down for planned work to integrate pumping station software into the site SCADA. When a works is taken out of supply this can present an opportunity for specialist maintenance which would otherwise be difficult or impossible to complete. In this instance, a specialist valve contractor was employed to ‘rattle’ one of the high lift pump outlet valves. However, a risk assessment for the work did not consider any water quality considerations. This report has highlighted previously the need to carry out water quality risk assessment on any operation to avoid being the cause of an incident.
When the works was restarted high turbidity was recorded and the site automatically shut down. This is a failsafe control to protect public health. Attempts to flush the turbidity were unsuccessful, and the site was run to waste. Further restarts were delayed due to faults with the sodium bisulphite dosing which continued to dose while the works was shut down. This additionally required multiple attempts to flush the high turbid water and the construction of a temporary run to waste facility. As a consequence, downstream reservoir levels ran low and 130,920 consumers in the Rownhams area experienced loss of supply or discolouration between 18 and 31 December 2024.
This is not the first time that a loss of supply event occurred at Southern Water which was caused by work being undertaken by contractors on company sites. A previous event was also caused by poor management of contractors. As part of the investigation into this event, the company stated it would “review arrangements for management of contractors at site to make sure the correct level of supervision is in place” to prevent a recurrence. Recommendations were made for the company to revisit its arrangement for the management of contractors and subcontractors on site. Further enforcement may be issued if there is a recurrence of events of this nature involving contractor management.
The company rezoned the area to minimise the impact of loss of supply, and bottled water stations, bottled water deliveries and tankers were utilised. However, there were multiple issues with the provision of alternative supplies and given similar issues with previous loss of supply events associated with Testwood works, the Inspectorate has now issued a Section 19 undertaking to improve resilience at the works and improve provision of alternative supplies. The works already has a Final Enforcement Order in place for improvements to the treatment plant.
Other notable events
Southern Water – Brede WSW High Chlorate August 2024
Ongoing maintenance is essential when dealing with drinking water infrastructure. However, with any live site scheduling work can be difficult if the very equipment requiring maintenance must stay operational. In which case appropriate plans must be put in place and it should not be deferred.
On such situation arose when pipework on the main hypochlorite dosing pumps at Brede works began to leak filling the bund underneath the main hypochlorite storage tank. The leaking dosing lines had been a known since at least January 2024 and not acted upon for months. Instead, the hypochlorite in the bund was being tankered away from the site approximately once a month by a third-party contractor. A change in procedures by the third-party contractor outside of the companies control and with no mitigation in place led to a delay in the removal of the bund contents. To prevent the bund overtopping the company decided to return the contents of the bund to the dirty wash water tank where it could be blended with backwash water and returned to the works inlet on three separate occasions for a total of three hours and 45 minutes.
A risk assessment by the company underestimated of the pumping rate, the chlorine concentration and the bund size. In addition, the risk assessment, while it considered trihalomethane (THM) formation as a risk, did not consider chlorate as a risk and was focussed on avoiding an environmental pollution incident. This was not putting drinking water quality first.
Approximately two buckets of dechlorination tablets were added to the hypochlorite to reduce the risk of THM formation, however the dose was not calculated, nor were subsequent chlorine levels measured. These tablets were not approved for use under Regulation 31. This was not putting drinking water quality first.
Between 29 July and 1 August 2024, routine samples were taken from the final treated water sample point at Brede works, from Fairlight Ore service reservoirs (SR) one and two and Warren Fairlight and Udimore reservoirs. Results were obtained between 4 and 6 August 2024 reporting chlorate concentrations of 735 µg/L and 921 µg/L from Fairlight Ore 1 and 2 reservoirs, 695 µg/L from Warren Fairlight reservoir, 415 µg/L from Udimore and a chlorate result of 1,340 µg/L from Brede final treated water. This outcome did not consider water quality.
The company completed a public health risk assessment to understand whether illness was likely to occur at the concentrations supplied. This assessment concluded that the risk of illness was low. UKHSA completed an assessment of public health risk which also concluded that the risk to public health at the concentrations seen and time of exposure was low. A formal investigation was mounted by the Inspectorate which included an audit of the works, witness statements from company staff and issued consumer questionnaires.
National conditions of use for electrolytically generated sodium hypochlorite state that the treated water must not contain chlorate greater than 700 µg/L. Additionally, unapproved dechlorination tablets were used prior to returning hypochlorite to the works inlet.
As such, the Inspectorate considered that there was evidence that offences under regulation 33(3) may have occurred and a warning letter was issued to the company. Water companies should take note that failure to maintain drinking water assets has serious outcomes and must be prioritised to protect public health.
Southern Water – Wingham – Nitrates above PCV April 2024
Nitrate occurs naturally in all surface water and ground water although higher concentrations tend to occur only where fertilisers are used on the land. It is produced during the natural decay of plant matter in soil. Rainfall washes nitrate out of the soil and into surface water such as lakes, rivers and streams. Nitrates can also seep down through the soil and be found in groundwater. Whilst it is generally low in waters in England, very high amounts of nitrate in drinking water can cause adverse health outcome in very young children. It is therefore a tightly regulated parameter upon which the standard is based on the World Health Organisation’s guideline value for drinking water, which is 50 mg/L.
On 20 April 2024, Southern Water was informed by its laboratory service that two nitrate samples had exceeded the prescribed concentration for nitrate of 50 mgNO3/L. One of these had been collected on 19 April 2024 from the treated water tap at Wingham works, with a nitrate concentration of 50.5 mgNO3/L. The other had been collected from a reservoir downstream of the works and reported a nitrate concentration of 51 mgNO3/L. This service reservoir is normally supplied from Wingham works. In response to these sample results, the company rezoned the service reservoir onto a supply from a different works.
The event was caused by the reliance on a single nitrate monitor at the works, whose readings had drifted downwards and was therefore providing inaccurate readings, resulting in the company failing to prevent Wingham works from supplying wholesome water with a nitrate concentration within the regulatory limit. This is not putting drinking water quality first because critical control points must have appropriate calibration on health-based parameters and preferably a secondary system to identify risk early. While it may be considered that laboratory analysis represents a secondary system, the company had experienced two other events linked to elevated nitrate concentrations in the previous 12 months. As the site was a known risk a secondary monitor would have been a minimum mitigation.
Following the Wingham event, the Inspectorate recommended that the company reviews the maintenance / calibration of nitrate monitors and installs additional validation monitors at all of its sites which are potentially at risk of breaching the regulatory limit for nitrate. The Inspectorate has previously issued a notice for the site requiring the company to install and commission ion exchange treatment for nitrate removal by 31 December 2025 securing the supply for the future.
Southern Water – Hastings loss of supply May 2024
In the early morning of 2 May 2024, Southern Water’s Beauport works shut down and could not be restarted as no raw water was being received from the Darwell raw water reservoir.
The company received 731 consumer contacts between 2 May and 8 May 2024 with 718 of these reporting loss of supply. The event was caused by a burst on the 800 mm concrete raw water main between the Darwell raw water reservoir and Beauport works.
The company previously applied for and was granted planning permission to replace the main in 2006. The company state in the non-technical summary document accompanying the planning application that the pipeline is of strategic importance to the continued security of drinking water supply to the Hastings area. The non-technical summary also states that over the past few years (prior to 2006) the pipeline suffered from a number of bursts and is now approaching the end of its useful life and that taking no action is not an option.
Due to the recurring theme of loss of supply/supply resilience associated with past events, a similar event will most likely recur until the company implements improvements to its supply system and that enforcement is now necessary to secure actions to prevent a reoccurrence. To ensure the company acts upon this high priority main, the Inspectorate has now issued a Section 19 undertaking for the main under SEMD.
Companies are reminded that critical assets such as raw water mains must be maintained and replaced where the asset is repeatedly failing causing a loss of supply.
Anglian Water – Welton works – Clostridium perfringens detections December 2024
Welton Works is a groundwater site supplying part of the Grimsby Skegness and the company detected clostridia on 6 June and 23 June 2024 and three coliform and one E. coli detection from 2023. Clostridium perfringens is used as an indicator species for historic and/or intermittent faecal contamination in drinking water. The size of Clostridia spores means that they can be a useful surrogate for Cryptosporidium and their presence on a system with a physical barrier process such as filtration may indicate that it has been less than effective and, consequently, the supply may be at risk from Cryptosporidium (Technical guidance on Microbiological Contaminants, Drinking Water Quality Regulator for Scotland).
The company considered that “The root cause of the UV outlet Clostridia is not thought to be due to filter performance.” However, a review by the Inspectorate noted that the individual filter flow trends on both 10 November and 20 December, at the exact time the samples containing the Clostridium perfringens were taken, RGF 3 was undergoing a filter backwash. The residence times in the filters, contact tank, new reservoir and old reservoir North/South equates to approximately 23 hours. For both Clostridia detections in November and December, RGF2 was undergoing a backwash approximately 23 hours prior to the time of the sample being taken.
These anomalies and the increase in turbidity being observed following a filter wash are signs of breakthrough at this stage of the treatment process. The company has been aware of these filter performance issues for some time and following a minded to consider enforcement within the audit assessment letter, the company provided reassurances to the Inspectorate that focussed investigations and appropriate remedial actions would be taken in a timely fashion
The Inspectorate was critical that the RGFs are likely to be outside of the scope of filtration performance required at this site since without individual turbidity monitors and head loss monitors on each filter, the filter performance cannot be verified. Five separate confirmed Clostridia detections lead to the potential that adequate filtration is not being achieved at Welton works. Similarly critical was the conclusion are the log reduction credits which are being assigned to the filters because the company cannot adequately show compliance with the requirements for the preliminary treatment of water prior to disinfection
The company has installed UV treatment at Welton works as an additional safeguard but not assigned it as part of the disinfection process at the treatment works, and Ct is met with chlorination only which is not commensurate with the function of the process or the intent of the regulation.
The Inspectorate provided the company with numerous occasions and ample opportunity to address the ongoing issues at Welton works. Consequently a Regulation 28(4) Notice for Welton works to secure compliance with bacteriological standards for drinking water quality was issued on 13 February 2025.
Yorkshire water – Longwood – Loss of ferric sulphate dosing July 2024
Ferric sulphate is a versatile and effective chemical used in water treatment the coagulation and flocculation of particles reducing turbidity in water ready for the next step of treatment which is filtration. Without coagulation, turbidity rises making it less efficient for filters to remove contaminants.
An investigation into recent data trends from the works revealed a loss of ferric sulphate dosing which had occurred on 3 July 2024. The automated coagulant control system was in a fault state as there was no flow. To rectify the issue the control system was stripped and cleaned. However, on completion of the work, it was noticed that the flocculation stirrers had ceased operation and the ferric dosing pumps were not running. Attempts to restart the pumps caused the shutdown alarm to initiate and reset within 600 seconds. As a result, the automatic shutdown did not occur and the works was shutdown manually.
The works was restarted at 15:00 on 3 July 2024. Later that evening, the turbidity from the rapid gravity filters started to increase. The inlet flow to the works was reduced and it was concluded that the rise in RGF turbidity was likely as a result of the works shutdown earlier that day. The turbidity was monitored and once it had reduced, inlet flow was increased again. Subsequent discussions with the site team confirmed that they had made a decision not to run the site to waste following the restart of the works because the turbidity levels were not considered sufficiently high to require it.
On 4 July 2024, Yorkshire Water reported a compliance sample from the works which contained coliform bacteria at a concentration of 4 per 100 ml. The impact of the connected circumstance of the coagulation failure and the the decision not to run the non-coagulated water to waste provides a learning to companies of the criticalities of such decisions in the absence of a water quality lens.
The Inspectorate gave a recommendation for the training related to the escalation of critical treatment processes to be reviewed to ensure escalation procedures are followed and documented. This serves as a reminder to water companies of the importance of robust escalation practices in safeguarding water quality.
United Utilities – Lightshaw – consumer contacts July 2023
The importance of communication by companies about drinking water when there are changes are critical to maintaining confidence in drinking water. This is because consumers notice even slight changes in their drinking water and become concerned if there is a change which is unkown to the consumer, even if the drinking water as supplied is perfectly safe to use.
This event occurred following a planned change of source water by United Utilities at a site supplying consumers in the areas of St Helens and Wigan in July 2023.
Lightshaw works was returned to supply on 21 July 2023. One of the areas affected was a relatively new district metered area (DMA) that that was established between 2022 and 2023.
Between 24 July and 6 September 2023, the company received 120 contacts from consumers in water supply zones (WSZ) 120 and 125, expressing water quality concerns. The company also received a total of 366 written complaint letters from consumers located in the new DMA. Due to these complaints the company rezoned the network in September 2023 to supply that DMA from another zone fed from the Manchester ring main.
The change in source is an action that is undertaken by the company from time to time. While both sources provide wholesome water, the difference in source water chemistry results in a noticeable change in appearance, taste or odour for consumers. This can be managed by effective and timely consumer communications to pre-warn them of the change. Although the company carried out a risk assessment before returning Lightshaw works to supply after the change of source, the risk assessment failed to adequately consider the effect of source water change on consumers, especially those who had not previously received a supply from Lightshaw works. The company did send proactive communications to consumers to inform them of a planned change to the water supply, however the reassurance was inadequate and did not reach all consumers affected.
The Inspectorate carried out consumer questionnaires and took statements that provided evidence that consumers had rejected the water for drinking, cooking, and washing even though the water was perfectly safe to use. Consequently, the requirements of the regulations require a conclusion that the company had supplied unwholesome water following the change in source for Lightshaw works because it imparted a noticeable change to the appearance, taste and odour of the water supply which consumers did not find acceptable.
The company were issued with a warning letter on 4 July 2024. The event highlights the importance of comprehensive risk assessments and effective consumer communication when altering source water supplies. This also underscores the need for better anticipation of consumer acceptability issues, targeted communications, and more robust implementation of lessons learned from past incidents when considering future changes.
Thames water – Fuel contamination in Bramley, Guildford
Petrol and diesel create problems for drinking water pipes as hydrocarbons can pass through plastic mains pipes and create an odour in water at extremely low levels. One such situation arose when a long running and high-profile event concerning low level contamination of the mains supply with fuel, that is benzene occurred in Bramley, Guildford.
In August 2023, Thames Water were made aware of a significant historic fuel leak from a tank at a petrol station in the Bramley area. Due to the known risk of migration of hydrocarbon compounds from the soil through some water pipework materials, a review of local consumer contacts was carried out. It did not indicate that the fuel leak had impacted on water quality in the area, but investigatory sampling was carried out and a hydrant chamber was found to have a fuel odour, although a flush of the main confirmed no odour issues with the water supply itself.
No further issues were experienced until a consumer reported a ‘white spirit’ taste and odour in October 2023. Analytical results identified fuel-related hydrocarbon compounds above aesthetic operational levels, but below short-term health limits at the property and at a neighbouring property. Advice not to drink the water was provided to the two properties and bottled water was delivered by the company. In January 2024 the communication pipework to the two properties was replaced with specialist barrier pipework which is impervious to fuel transmission through the pipe wall. The restriction of use advice was rescinded following satisfactory confirmatory samples at one property on 9 February and the other on 5 March 2024.
Thames Water proactively sampled the wider area in October 2023 through which low levels of hydrocarbons were detected. Thames Water determined that no short or long-term health impacts were anticipated at these levels, but the company took the decision to continue water quality analysis and monitoring around Bramley. The company also continued engagement with the Local Authority, UKHSA (UK Health Security Agency) and third-party environmental consultants in relation to the fuel leak and the steps to remediate the contaminated land.
A water quality sample collected in April 2024 identified concentrations of benzene above the prescribed concentration (PCV) in a public building in close proximity to the historic fuel contamination. Analytical results of further samples taken in late April and early May 2024 were below the prescribed concentration.
A hydrocarbon odour was detected by one of the three analysts on the odour testing panel from a sample collected from the public building on 14 May 2024 (considered a pass under the standard methodology). However on risk assessing the findings, the company issued restriction of use advice for the property. Subsequent analysis of the same samples taken on 14 May 2024 identified benzene above the PCV and alternative water supplies were provided to the public building.
Samples collected on 28 May 2024 from another location in Bramley contained benzene above the prescribed concentration (PCV). The risk assessment was updated to reflect this deteriorating trend in hydrocarbon concentrations in the area, and the company decided to issue do not drink advice to a wider area of Bramley containing 622 properties on 30 May 2024. Letters informing consumers were hand delivered to affected properties. Bottled water stations were opened the same day with bottled water delivered to vulnerable consumers. Arlington tanks were deployed to provide an alternative water supply to local schools.
The company continued to monitor water quality, and reviewed remediation options. Pressure management plans were implemented to contain the issue to as few properties as possible. Routine flushing was also implemented to reduce the hydraulic residence time and therefore the concentration of benzene in the water mains.
Sections of MDPE water main that were in close proximity to the contaminated ground and therefore subject to hydrocarbon permeation were replaced with barrier pipe. This was a complex operation as additional safety controls were needed to address combustion risks, this was completed and commissioned on 26 June 2024.
The issue of the wider restriction of use notice to properties in Bramley attracted significant media interest. The company issued media statements throughout May, June, and July 2024. To keep consumers informed, a frequently asked questions web page was produced, and laboratory data was also shared with weekly updates.
Following remediation efforts, verification through water quality samples and consultation with public health stakeholders, the restriction of use notice in Bramley was rescinded on 3 July 2024.
Thames Water’s proactive monitoring programme since October 2023 ultimately led to the identification of the mains contamination from a third-party source and contributed to establishing an appropriate course of action (installing barrier pipe) to address the issue. The company continues to risk assess and monitor the situation in Bramley. The analytical results from 3 July to 19 September 2024 showed some very low levels of hydrocarbons in some samples. However, analysis since 24 September 2024 shows no further detection of fuel-based hydrocarbons in the water supply .