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Poly and Perfluorinated Alkyl Substances (PFAS)

Background

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are a group of synthetic chemicals that include PFOA, PFOS and other related substances. They have been used widely for a range of purposes from industrial to household products, that have had or continue to have widespread use in England and Wales. Certain PFAS are known to have the potential to persist in the environment, including in water and some have shown the capability to bioaccumulate. This has raised a keen interest in better understanding their potential impact on the environment and toxicity.

Research and guidance

The Inspectorate provides general guidance on PFAS.

In March 2025, a consolidated guidance document was issued to water companies detailing the Inspectorate’s requirements regarding PFAS monitoring, risk assessment, and strategy in relation to public water supply systems.

The World Health Organization (WHO) has produced a guidance document on PFOS and PFOA in drinking water.

Defra have produced a policy paper PFAS Plan: building a safer future together – GOV.UK

Research into the efficacy of various treatment types on PFAS removal has been published on the Inspectorate’s website, see link to research page. Whilst efficacy varies by type of PFAS, treatment process, and source water characteristics, the research shows that PFAS can be effectively removed from water sources using known water treatment processes. Key findings of the research:

  • Removal performances of nanofiltration and reverse osmosis membranes is typically above 90% for most PFAS.
  • Conventional GAC (Granular Activated Carbon) is effective at removing >6 carbon chain PFAS.
  • Short chain carboxylic acid PFAS were the most challenging to remove.
  • The background water matrix impacts removal, with PFAS more effectively removed from groundwater over upland water and lowland water.

Further research and data gathering on PFAS in water sources and drinking water supplies is ongoing. As we learn more our guidance will become more informed.

Various agencies have commissioned research into the toxicology of PFAS. Local authorities should consult the UK Health Security Agency (UKHSA) or Public Health Wales (PHW) being the lead public health agencies respectively for more information on PFAS in water used for domestic purposes, particularly where analysis confirms their presence, as health advice will be informed by the specific substance/s found, and their concentrations. It may be necessary for local authorities to keep an open dialogue with UKHSA or PHW on PFAS.

Private water supply risk assessment

Due to the wide range of PFAS sources entering the environment, and their persistence, it is recommended that local authorities consider initially any inherent potential catchment sources of PFAS which may present risks to private supplies in their area. This should be undertaken as part of their regulation 6 risk assessments, the outputs from which should then inform their monitoring plans for each supply going forward.

When evaluating potential sources of PFAS contamination in drinking water catchments, research has identified a diverse array of contributors, which include but are not limited to:

  • Fire stations and training sites.
  • Pollution incident sites.
  • Mechanics.
  • Air transport sites.
  • Military bases.
  • Chrome plating sites.
  • Carpet, leather, paper, and textile manufacturing.
  • Landfill sites.
  • Wastewater treatment works.
  • Land spreading of sewage sludge and other solid waste.

However, detectable concentrations of PFAS have been found in water where there is no apparent connection to any of these. As such, local authorities should also consider the risk of unknown sources of PFAS in private water supplies, where the potential for their presence may exist.  Where public supplies are in the vicinity, dialogue with the water company may identify sources and presence of PFAS in the same supply source, allowing more targeted investigation.  Where they are found, due to their persistence and mobility in the environment, the potential area and number of supplies that could be affected, should be considered. Local authorities are advised to gather and utilize intelligence from other relevant environmental departments, such as land pollution teams, to further inform the risk assessment. Water companies are also encouraged to share relevant information with local authorities.

The risk assessment should consider the potential presence of PFAS throughout the source to tap supply chain, taking account of any existing mitigation that already may be in place, such as existing treatment.

It should be noted that by the end of 2026, the Environment Agency’s (EA) PFAS multicriteria Geographic Information System (GIS) prioritisation map will be made available to all public sector bodies across England, including local authorities, to support environmental risk assessment and decision-making. Furthermore, the EA will explore the development of a dedicated interactive website by the end of 2027 to enhance accessibility and usability.

Where PFAS has been detected in a private water supply, local authorities are advised to consult UKHSA to establish whether this constitutes a potential danger to human health.  If it does, they must promptly take appropriate steps, as per regulation 15 (17 in Wales) to ensure that people likely to consume water from it:

  • Are informed that the supply constitutes a potential danger to human health.
  • Where possible, are informed of the nature of the potential danger.
  • Are given advice to allow them to minimise any potential danger.

Investigations

The presence of PFAS in a private water supply is to be regarded as unwholesome where it is a concentration or value that would constitute a potential danger to human health (regulation 4(1)(a)). Any private water supply that is a potential danger to human health by virtue of PFAS must be investigated by the local authority in accordance with regulation 16 (18 in Wales). 

In England, the regulations require the investigation to establish the cause of the unwholesome water.

In Wales the regulations require the investigation is establish the cause of any PFAS failure.

An investigation will, in most instances, require the supply to be monitored to establish (a) the root cause (b) where in the source to tap supply chain PFAS is present, (c) which PFAS types are present, and (d) at what concentrations they are found, including the maximum and minimum concentrations over any sampling duration. Monitoring programmes should be established on a case-by-case risk basis at the discretion of local authorities.  Sampling must be carried out to the ISO17024 or ISO17025 standard in accordance with the regulatory requirements.

The outputs from the investigation, notably the monitoring results to date, will determine the necessary actions that the local authority must carry out to meet the requirements of regulation 16 (18 in Wales). This must consider the potential danger to human health that the presence of any PFAS detected may present.

As part of the investigation, local authorities are advised to consult the United Kingdom Health Security Agency (UKHSA) or Public Health Wales (PHW) to establish whether the PFAS detected, and the concentration at which it was found, presents any actual or potential health risk if some continued use is proposed rather than serving a notice to cease use. UKHSA/PHW can if required, assess the potential health implications to consumers using the information provided by the local authority. This will need to include the analytical results (types of PFAS, concentrations and dates), and information from the risk assessment about the supply, including how the water is used, any treatment (and any changes in PFAS concentration), the volume of water consumed, number of people/properties on the supply, and if there are any vulnerable or transient consumers using the supply. UKHSA/PHW may determine that the water should not be used for one or more domestic purposes.

Enforcement

Should the local authority conclude from their risk assessment and or investigation that a supply presents a potential danger to human health they must serve a notice in accordance with the conditions specified in regulation 18 (20 in Wales).

The notice must require the prohibition or restriction of the supply in a manner that is appropriate to the PFAS type and the risk that this presents. It must also set out what corrective actions must be taken to safeguard human health, restore the wholesomeness of the supply, and maintain the continued wholesomeness of the water following restoration.

Analysis

Laboratory capability and capacity is expanding, with analytical methods being developed to enable detections of a larger range of PFAS, at ever lower concentrations. Local water companies may be able to provide more up to date information on the PFAS analytical capabilities in their areas.

The United Kingdom Accreditation Service (UKAS) is the organisation responsible for accrediting the analytical capabilities of laboratories.

The UKAS website lists laboratories currently accredited for PFAS analysis.

Local authorities should consult with laboratories to establish when there may be opportunity for PFAS analysis. In the first instance, it is important for local authorities to understand if any of their supplies are at high risk of the presence of PFAS. High risk supplies can then be prioritised for further action which may include sampling and analysis when it is available. Sources of data and information to help inform risk assessments include the Environment Agency, and local water companies, who are undertaking sampling and analysis of various environmental waters.

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