Whether water containing PFAS is safe to drink depends on the concentrations present and your personal circumstances. At the low levels found in most UK tap water, current regulatory science suggests the risk for healthy adults is low — but the precautionary principle is reasonable, particularly for vulnerable groups. This guide explains what we know and what we do not.

What are PFAS and why are they in water?

PFAS (per- and polyfluoroalkyl substances) are a family of over 4,000 synthetic chemicals that have been used since the 1940s in firefighting foam, non-stick cookware, waterproof clothing, food packaging, and industrial processes. They do not break down in the environment, hence the "forever chemicals" label. They have contaminated water sources globally, particularly near military bases, airports, and industrial sites where AFFF firefighting foam was used.

Current UK limits and enforcement

The UK does not currently have statutory legal limits specifically for PFAS in drinking water, unlike the EU (which introduced a 0.1 µg/l sum-of-20-PFAS limit in 2021) or the US EPA (which set maximum contaminant levels for six specific PFAS in 2024). The UK Drinking Water Inspectorate operates with a voluntary investigatory level (IL) of 0.1 µg/l for total PFAS.

Thames Water has active DWI improvement notices for exceeding this IL at certain treatment works. Other companies have also reported PFAS detections during enhanced monitoring programmes.

Health evidence: what do we know?

The health evidence for PFAS is significant but complex:

  • Higher PFAS exposure (substantially above current drinking water levels) is associated with increased risk of certain cancers, thyroid disruption, immune function changes, and developmental effects in children in occupational and heavily contaminated community studies.
  • At the low levels currently found in UK tap water, the Committee on Toxicity (COT) assessed in 2022 that the risk for healthy adults from drinking water alone is low.
  • PFAS bioaccumulate in the body over time, so long-term cumulative exposure — from multiple sources including food, cookware, and clothing — is the appropriate frame, not just water.

Who is most at risk?

Regulatory bodies globally identify the following groups as warranting extra precaution:

  • Pregnant women (PFAS can cross the placenta)
  • Breastfeeding mothers (PFAS are present in breast milk at elevated levels in high-exposure populations)
  • Infants and young children (greater relative fluid intake and developmental sensitivity)
  • People with compromised immune systems

The precautionary principle

Given evolving science and the absence of UK statutory limits, many water quality experts apply the precautionary principle: even if current levels are assessed as low risk, reducing PFAS exposure where it is affordable and practical is reasonable.

The most effective domestic PFAS reduction methods are:

  • Reverse osmosis (RO): NSF/ANSI 58-certified systems remove 95–99% of PFAS.
  • Solid block carbon filters with NSF P473 certification: Provide meaningful but less complete PFAS reduction than RO.

Enter your postcode to check whether your supply zone has active PFAS improvement notices.