- Drinking Water 2025 – Summary of the Chief Inspector’s report for drinking water in Wales
- Foreword
- Introduction
- Water supplies and testing
- Compliance with standards
- Learning from compliance failures
- Learning from events
- Consumer contacts
- Asset health
- Water safety planning and risk assessment
- Poly and perfluoroalkyl substances (PFAS)
- Audit programme
- Recommendations
- Enforcement
- Security and Emergency Measures Direction - SEMD
- Network and Information Systems - NIS
- Materials in contact with drinking water (Regulation 31)
- Research publications
- Whistleblowers
- Working with stakeholders
Poly and perfluoroalkyl substances (PFAS)
PFAS are a group of man-made compounds based on chains of carbon and fluorine atoms. They contain at least one fully fluorinated methyl or methylene group. The carbon-fluorine bond is very strong, meaning these compounds do not degrade easily in the environment. They are resistant to grease, oil, water and heat, and have been used in a wide range of products, including stain- and water-resistant fabrics and carpets, paints, firefighting foams, cookware and food packaging.
The production, use and disposal of these substances means they are now widely detected in the environment. Because of their persistence, they may eventually be found in water, including groundwater and surface water.
The Inspectorate updated its guidance to industry in August 2024 on requirements to submit sample results and summary risk assessment information for PFAS, and this remains a major focus. Companies have continued targeted sampling strategies focused on sites most likely to be at risk from PFAS contamination. In 2025, companies across the industry collectively carried out more than 666,000 analyses for individual PFAS. In total, more than 2.3 million analyses have been performed since 2012, providing a significant dataset to support understanding of the challenges for drinking water. Analysis peaked in 2024, when more than 777,000 tests were carried out. The reduction in 2025 reflects a more focused and targeted sampling programme based on validated risk assessments.
PFAS tiers are now applied to any PFAS chemicals of interest detected in the final or raw water. PFAS chemicals of interest are identified in the parameter list (Annex C of the Information Direction). The actions companies should be taking for the three tier levels is available in our most recent guidance – DWI_PFAS-Guidance_Mar_2025.pdf
Sites are classified as:
- Tier 1 where PFAS concentrations are <0.01 µg/L.
- Tier 2 where PFAS concentrations are <0.1 µg/L.
- Tier 3 where PFAS concentrations are ≥0.1 µg/L
Monitoring by water companies highlighted a further PFAS compound of potential concern; 6:2 fluorotelomer sulfonamide alkylbetaine (6:2 FTAB). This compound has been added to the parameter list and companies are expected to initiate monitoring and reporting for this parameter as soon as practicable. Companies are also expected to consider the effect of combined concentrations of the PFAS chemicals of interest identified in the parameter list. As such, the requirement to implement a prioritised mitigation methodology to progressively reduce PFAS concentrations in drinking water has been further extended to include combined PFAS on a ‘sum of’ basis. Companies have now implemented reporting for the ‘sum of PFAS’ based on the 48 named PFAS compounds in the parameter list. Where sites now fall into tier 2 or 3 for the sum of parameter these sites should be rolled into the existing site prioritisation approach based on their relative classification and an appropriate risk reduction strategy should aim to progressively reduce PFAS concentrations in drinking water.
Analysis targets source water because this provides information on the hazard and informs the mitigation required, whether through blending, removal of the source water or treatment. During 2025, there were no tier 2 or tier 3 samples in Wales, with 49 positive samples in tier 1. This demonstrates that the current industry strategy for mitigating PFAS risks is working effectively to protect consumers.
| Tier | Raw water tests | Treated water tests | Total |
|---|---|---|---|
| Tier 1 | 11,312 | 18,646 | 29,958 |
| Tier 2 | 42 | 42 | |
| Tier 3 | |||
| 11,354 | 18,646 | 30,000 |
The most prevalent species detected in raw and treated water during 2025 was perfluorobutanoic acid (PFBA), accounting for 34% of all positive sample results. The table below sets out the other parameters detected.
| Parameter name | Tier 1 | Tier 2 | Tier 3 | Total |
|---|---|---|---|---|
| PFBA | 9 | – | – | 9 |
| PFBS | 5 | – | – | 5 |
| PFOA | 5 | – | – | 5 |
| 6:2 FTSA; 6:2 FTS | 3 | – | – | 3 |
| 6:2 FTAB | 2 | – | – | 2 |
| 11CL-PF3OUdS | 1 | – | – | 1 |
| EtFOSAA | 1 | – | – | 1 |
| FOSA | 1 | – | – | 1 |
| MeFOSAA | 1 | – | – | 1 |
| PFDA | 1 | – | – | 1 |
| PFDoDA | 1 | – | – | 1 |
| PFDS | 1 | – | – | 1 |
| PFecHS | 1 | – | – | 1 |
| PFHxA | 1 | – | – | 1 |
| PFOS | 1 | – | – | 1 |
| PFUnDA | 1 | – | – | 1 |
| PFUnDS | 1 | – | – | 1 |
| Total | 36 | – | – | 36 |
The most prevalent species in raw and treated water during 2025 is PFBA with 34% of all positive sample results, the below table sets out all the other parameters detected.
| Parameter name | Tier 1 | Tier 2 | Tier 3 | Total |
|---|---|---|---|---|
| PFBA | 16 | – | – | 16 |
| PFBS | 11 | – | – | 11 |
| PFUnDA | 4 | – | – | 4 |
| PFDA | 3 | – | – | 3 |
| PFDS | 3 | – | – | 3 |
| EtFOSAA | 2 | – | – | 2 |
| PFOS | 2 | – | – | 2 |
| 11CL-PF3OUdS | 1 | – | – | 1 |
| 6:2 FTSA; 6:2 FTS | 1 | – | – | 1 |
| 9Cl-F3ONS | 1 | – | – | 1 |
| PFDoDA | 1 | – | – | 1 |
| PFHxA | 1 | – | – | 1 |
| PFNS | 1 | – | – | 1 |
| PFOA | 1 | – | – | 1 |
| PFUnDS | 1 | – | – | 1 |
| Total | 49 | – | – | 49 |