- Drinking Water 2025 – Summary of the Chief Inspector’s report for drinking water in England
- Foreword
- Water supplies and testing
- Compliance with water quality standards
- Learning from microbiological failures
- Learning from turbidity failures
- Learning from chemical, taste and odour failures
- Learning from pesticide failures
- Asset health and service reservoir integrity
- Consumer contacts
- Drinking water quality events
- Water safety planning and risk assessment
- Perfluoroalkyl and polyfluoroalkyl substances (PFAS)
- Audit programme completed by the Inspectorate
- Air valve audits
- Enforcement, transformation and recommendations
- Materials in contact with drinking water (regulation 31)
- Security and Emergency Measures Direction - SEMD
- Network and Information Systems - NIS
- Research publications
- Whistleblowers
- Working with stakeholders
- Annex A – Number of tests carried out by companies
- Annex B – Compliance with standards
- Annex C – Compliance failures and events
Perfluoroalkyl and polyfluoroalkyl substances (PFAS)
Perfluoroalkyl and polyfluoroalkyl substances (PFAS) remain a significant focus for the Inspectorate because of their persistence in the environment and their potential to affect drinking water sources. The Inspectorate updated its industry guidance in August 2024, with a further update issued in 2025, setting out expectations for sample reporting, summary risk assessment information and prioritised mitigation. Companies have continued to use targeted sampling strategies to focus on sites most likely to be at risk from PFAS contamination. In 2025, companies across England and Wales undertook more than 666,000 analyses for individual PFAS. Since 2012, more than 2.3 million analyses have been completed, providing a substantial dataset to support understanding and management of PFAS risks in drinking water.
The Inspectorate’s PFAS guidance requires companies to apply the tier framework to all PFAS of interest listed in Annex C of the Information Direction where they are detected in raw or final water. The 2025 guidance consolidated the actions expected at each tier level and reinforced the need for companies to assess results in the context of source risk, treatment capability, blending arrangements and consumer exposure.
Sites are classified as:
- Tier 1 where PFAS concentrations are <0.01 µg/L;
- Tier 2 where PFAS concentrations are <0.1 µg/L; and
- Tier 3 where PFAS concentrations are ≥0.1 µg/L
Monitoring by water companies has also highlighted 6:2 fluorotelomer sulfonamide alkylbetaine (6:2 FTAB) as a PFAS of potential concern. Companies are now expected to consider both individual PFAS results and the combined concentration of PFAS of interest. The requirement to implement a prioritised mitigation methodology has therefore been extended to include the “sum of PFAS” based on the 48 named substances in the parameter list. Where a site falls into Tier 2 or Tier 3 on a sum-of-PFAS basis, it should be incorporated into the company’s existing site prioritisation approach, with a proportionate risk reduction strategy designed to progressively reduce PFAS concentrations in drinking water.
PFAS monitoring is focused on source water because this provides information on the hazard and informs the most appropriate mitigation, which may include source substitution, blending, treatment or removal of an abstraction from supply. In 2025, two treated water samples supplied to consumers were reported in Tier 3. In raw water, 353 samples from abstractions were reported in Tier 3. These findings indicate that PFAS remains a source-water challenge, but also demonstrate the importance of the current industry strategy in identifying, prioritising and mitigating risks before they reach consumers.
| Tier | Raw water tests | Treated water tests | Total |
|---|---|---|---|
| Tier 1 | 373,812 | 234,233 | 608,045 |
| Tier 2 | 11,810 | 4,385 | 16,185 |
| Tier 3 | 353 | 2 | 355 |
| Total | 238,650 | 385,975 | 624,595 |
Affected sites
Where PFAS is identified, companies are expected to act in accordance with the Inspectorate’s risk prioritisation strategy. This includes confirming the source and extent of contamination, assessing treatment and blending capability, identifying potential consumer exposure and implementing proportionate mitigation to reduce concentrations over time.
In 2025, two Tier 3 PFOS detections in treated water were reported from the same treatment works operated by Southern Water. Previous detections had also been reported from this source, with two in 2022 and three in 2023. The works is relatively small, supplying approximately 1.7 ML/day, and is located close to a disused airfield. Water from the works is blended within an extended distribution network before reaching consumers’ taps.
Sum of PFAS
Sampling undertaken in early February 2025 identified a sum of PFAS concentration of 0.103 µg/L in treated water from Wessex Water’s Charlton Minety works. A subsequent sample collected in early March recorded 0.098 µg/L. The works supplies the Minety distribution system and Rodbourne works, where further blending occurs before supply to approximately 6,700 consumers. At the time of the event, the works did not include treatment capable of removing PFAS.
The company notified the Inspectorate promptly and confirmed that it relied on blending at Rodbourne to reduce PFAS concentrations before supply. However, this control was not supported by sufficiently robust verification or operational safeguards at the time. The company did not issue consumer advice, maintaining that subsequent marginally lower results did not warrant intervention. Longer-term options were already under consideration, including granular activated carbon (GAC) treatment and a new treatment works at an alternative location, but these were not then programmed for completion until 2035.
The Inspectorate concluded that water supplied during the event had PFAS concentrations above the published guidance and was therefore potentially unwholesome. Historical monitoring showed that this was not an isolated occurrence, with multiple results above the Tier 3 sum-of-PFAS threshold since mid-2024, including a peak of 0.205 µg/L. Although the March 2025 guidance formally extended the PFAS approach to the sum of 48 PFAS, the company had been calculating this value since June 2024. The risk was therefore evident before the event and should have informed earlier mitigation planning.
The Inspectorate required enhanced monitoring at Charlton Minety and Rodbourne works to provide assurance that blending controls were effective. Daily fast-track sampling was sought, but laboratory capacity and turnaround constraints meant that weekly sampling was implemented. The Inspectorate also required blending arrangements to be verifiable and protected by safeguards to prevent supply above Tier 3 levels. The company subsequently introduced a blending protocol supported by software flow interlocks and was required to review all assets where blending is used to control PFAS concentrations.
The company’s regulation 28(4) notice was revised to accelerate mitigation. The deadline for the permanent solution was brought forward to 2031, and temporary granular activated carbon treatment was expedited. The first GAC pod was installed in November 2025 to treat water supplied directly to the Minety area, and a second pod was commissioned in May 2026. Following installation of the first pod, results were below the limit of detection or within Tier 1, apart from one February 2026 result marginally above Tier 3 that was reported as an event and attributed by the company to a sampling error between adjacent pre- and post-GAC taps.
The key lessons from this event are that elevated sum-of-PFAS results should trigger prompt escalation and intervention, rather than reliance on future capital schemes. Where blending is used as a control measure, it must be demonstrably effective, supported by robust monitoring, operational safeguards and clear trigger levels. The event also highlighted practical constraints in increasing PFAS monitoring frequency, particularly laboratory capacity and analytical turnaround times, which companies must consider when designing assurance arrangements. PFAS monitoring is risk-based and targeted towards sources and assets most likely to be affected. Results should therefore be interpreted in that context, because a higher proportion of samples is collected from higher-risk locations. Of the 989 treatment works in supply across England in 2025, Tier 2 concentrations were detected in treated water at 82 locations, representing 8.29% of sites. Tier 2 results remain below the Inspectorate’s health-based guidance value of 0.1 µg/L for the sum of PFAS, but companies are expected to take a precautionary approach and develop strategies to reduce PFAS concentrations at these sites over time.
| PFAS Tier | Raw water results | Treated water results | Total calculations |
|---|---|---|---|
| Tier 1 | 5,158 | 3,290 | 8,448 |
| Tier 2 | 1,337 | 850 | 2,187 |
| Tier 3 | 241 | 4 | 245 |
| Total | 6,736 | 4,144 | 10,880 |
Hanningfield sum of PFAS event
An event was reported at Hanningfield treatment works following detection of elevated PFAS in a sample collected on 6 October 2025. The sum-of-PFAS concentration was 0.106 µg/L, above the Tier 3 threshold of 0.1 µg/L. The result was largely driven by 6:2 fluorotelomer sulfonamide betaine (6:2 FTAB).
The elevated concentration was attributed to changes in raw water operation. Water from the River Blackwater was abstracted directly into the works rather than being blended with reservoir water from Hanningfield reservoir, because the proportion of reservoir water had been reduced in response to an algal bloom. Subsequent sampling showed PFAS concentrations reducing to Tier 2 levels, and catchment investigations indicated that the likely source of contamination was within the River Brain, a tributary of the River Blackwater.
The company undertook extensive sampling across the treatment works, supply zones and wider catchment, and engaged with relevant stakeholders. Although PFAS concentrations reduced after the event, evidence indicated that the existing treatment processes at the works were largely ineffective for PFAS removal. There was also evidence that ozonation may transform longer-chain PFAS compounds into shorter-chain species, which can be more difficult to remove using conventional treatment processes.
The company subsequently reverted abstraction towards Hanningfield reservoir water as raw water conditions improved. However, this operational change was driven by raw water quality considerations rather than by a defined PFAS mitigation strategy. The Inspectorate concluded that water supplied during the event was potentially unwholesome. Concerns were identified regarding the timeliness of sampling and analytical turnaround, the absence of a robust and effective PFAS treatment strategy, and the need for clearer evidence on treatment performance and laboratory capability. The Inspectorate is minded to take enforcement action requiring the company to strengthen PFAS risk management, improve sampling and reporting timeliness, develop effective mitigation measures and provide further evidence to prevent recurrence.
Raw water data – number of tests per tier greater than the limit of detection (LOD)
| Parameter | Tier 1 results | Tier 2 results | Tier 3 results | Total results |
|---|---|---|---|---|
| PFOS | 1449 | 636 | 125 | 2210 |
| PHFHxS | 1392 | 374 | 100 | 1866 |
| PFHxA | 1472 | 376 | 14 | 1862 |
| PFOA | 1480 | 165 | 13 | 1658 |
| PFBS | 1258 | 136 | 11 | 1405 |
| PFPA | 748 | 398 | 14 | 1160 |
| PFBA | 1085 | 63 | 1148 | |
| PFHpA | 764 | 45 | 14 | 823 |
| 6:2 FTAB | 120 | 166 | 9 | 295 |
| 6:2 FTSA; 6:2 FTS | 86 | 188 | 13 | 287 |
| PFecHS | 125 | 131 | 256 | |
| PFPS | 141 | 87 | 12 | 240 |
| FBSA | 94 | 83 | 14 | 191 |
| FHxSA | 40 | 102 | 14 | 156 |
| PFDA | 83 | 83 | ||
| PFNA | 72 | 72 | ||
| HFPO-TA | 62 | 2 | 64 | |
| PFUnDA | 56 | 56 | ||
| PFHpS | 38 | 16 | 54 | |
| 8:2 FTSA | 31 | 11 | 42 | |
| 9Cl-F3ONS | 34 | 34 | ||
| EtFOSAA | 33 | 33 | ||
| FOSA | 16 | 14 | 30 | |
| MeFOSAA | 29 | 29 | ||
| PFNS | 28 | 28 | ||
| PFDS | 16 | 2 | 18 | |
| PFDoDA | 14 | 2 | 16 | |
| NFDHA | 14 | 1 | 15 | |
| 11Cl-PF3OUdS | 10 | 1 | 11 | |
| PFTeA | 11 | 11 | ||
| HFPO-DA (Gen X) | 7 | 7 | ||
| PFDoS | 6 | 6 | ||
| DONA | 5 | 5 | ||
| MeFOSE | 5 | 5 | ||
| PFUnDS | 3 | 1 | 4 | |
| 5:3 FTCA | 3 | 3 | ||
| EtFOSE | 3 | 3 | ||
| MeFOSA | 3 | 3 | ||
| 3:3 FTCA | 1 | 1 | 2 | |
| EtFOSA | 2 | 2 | ||
| PFTrDA | 2 | 2 | ||
| 7:3 FTCA | 1 | 1 | ||
| PFHxDA | 1 | 1 | ||
| PFMOBA | 1 | 1 | ||
| Total | 10,844 | 3,001 | 353 | 14,198 |
Raw water data – number of tests per tier greater than the limit of detection (LOD) 44 out of 48 had positive detections in 2025, meaning that there were no positive detections for 4 PFAS species.
Treated water data – number of tests per tier greater than the limit of detection (LOD)
| Parameter | Tier 1 results | Tier 2 results | Tier 3 results | Total samples |
|---|---|---|---|---|
| PFHxA | 1165 | 116 | 1281 | |
| PFOS | 834 | 251 | 2 | 1087 |
| PFBS | 1056 | 21 | 1077 | |
| PHFHxS | 929 | 146 | 1075 | |
| PFOA | 873 | 58 | 931 | |
| PFBA | 877 | 52 | 929 | |
| PFPA | 642 | 150 | 792 | |
| PFHpA | 611 | 6 | 617 | |
| PFecHS | 197 | 16 | 213 | |
| PFPS | 181 | 3 | 184 | |
| FBSA | 161 | 4 | 165 | |
| 6:2 FTSA; 6:2 FTS | 83 | 74 | 157 | |
| 6:2 FTAB | 109 | 39 | 148 | |
| PFODA | 76 | 76 | ||
| FHxSA | 27 | 29 | 56 | |
| PFDA | 50 | 1 | 51 | |
| 8:2 FTSA | 48 | 48 | ||
| PFHpS | 43 | 1 | 44 | |
| PFUnDA | 42 | 1 | 43 | |
| EtFOSAA | 37 | 37 | ||
| PFNA | 35 | 1 | 36 | |
| PFNS | 32 | 32 | ||
| MeFOSAA | 31 | 31 | ||
| HFPO-TA | 30 | 30 | ||
| PFDS | 29 | 1 | 30 | |
| PFTeA | 24 | 24 | ||
| 3:3 FTCA | 22 | 22 | ||
| 9Cl-F3ONS | 22 | 22 | ||
| PFDoS | 20 | 20 | ||
| PFDoDA | 18 | 1 | 19 | |
| EtFOSE | 17 | 1 | 18 | |
| PFUnDS | 17 | 1 | 18 | |
| 11Cl-PF3OUdS | 17 | 17 | ||
| PFTrDA | 15 | 1 | 16 | |
| FOSA | 15 | 15 | ||
| MeFOSE | 15 | 15 | ||
| NFDHA | 14 | 14 | ||
| 5:3 FTCA | 13 | 13 | ||
| EtFOSA | 13 | 13 | ||
| 7:3 FTCA | 12 | 12 | ||
| MeFOSA | 12 | 12 | ||
| PFHxDA | 12 | 12 | ||
| HFPO-DA (Gen X) | 11 | 11 | ||
| 4:2 FTSA | 7 | 7 | ||
| DONA | 6 | 6 | ||
| PFMOPrA | 4 | 4 | ||
| PFEESA | 3 | 3 | ||
| PFMOBA | 3 | 3 | ||
| Total | 8,510 | 974 | 2 | 9,486 |
PFAS at treatment works
The detailed PFAS tables show that detections are concentrated at a relatively small number of higher-risk sites. This reflects the targeted nature of company monitoring, which focuses sampling on sources and treatment works where PFAS contamination is most likely. The Inspectorate therefore interprets the data alongside source risk, treatment capability, blending arrangements and company mitigation programmes, rather than as a simple measure of average national exposure.
| Company name | Total number of abstraction points | Actual number of affected abstraction points | Percentage affected | All company improvement programme issued? |
|---|---|---|---|---|
| Affinity Water Ltd | 237 | 9 | 3.80% | Yes |
| Anglian Water Services Ltd | 622 | 47 | 7.56% | Yes |
| Bristol Water Plc | 30 | 2 | 6.67% | Yes |
| Isles of Scilly* | 26 | 2 | 7.69% | |
| Northumbrian Essex and Suffolk Water | 120 | 4 | 3.33% | Yes |
| SES Water | 93 | 1 | 1.08% | Yes |
| Severn Trent Water Ltd | 347 | 1 | 0.29% | Yes |
| South Staffordshire Water Plc | 87 | 6 | 6.90% | Yes |
| Southern Water Services Ltd | 245 | 2 | 0.81% | Yes |
| Thames Water Utilities Ltd | 238 | 4 | 1.68% | Yes |
| United Utilities Water Ltd | 159 | 1 | 0.22% | Yes |
| Wessex Water Services Ltd | 342 | 3 | 0.88% | Yes |
*The Isles of Scilly are incorporated into the SWB notice
Although only a small number of treated-water samples were reported in Tier 3, Tier 2 detections remain important because they identify sites where PFAS concentrations require ongoing control and reduction. Companies with Tier 2 detections are expected to maintain clear risk assessments, understand the contribution from each source or treatment works, and set out proportionate mitigation to reduce PFAS concentrations over time.
Anglian Water remains the most notable company in this dataset. The Inspectorate currently has five notices and one undertaking in place requiring PFAS mitigation measures at Anglian Water sites. The notices were put in place during 2023 and 2024 and are generally due for completion around 2031. The undertaking was entered into voluntarily by the company and commits it to a broad programme of sampling, risk assessment, catchment investigation, source identification and proactive risk reduction to progressively reduce PFAS concentrations in drinking water.