Does Thames Water have a PFAS problem?

Yes. Thames Water has active DWI improvement notices related to PFAS at several treatment works drawing from the Thames catchment. It is investing in GAC treatment to reduce PFAS levels. Current levels are below UK legal limits.

Are PFAS in London water dangerous?

Current PFAS levels in London water are below UK legal limits and are assessed as low risk for healthy adults. At-risk groups (pregnant women, infants, immunocompromised) may wish to take precautionary measures such as using a certified RO or solid block carbon filter.

What filter removes PFAS from tap water?

NSF/ANSI 58-certified reverse osmosis systems are the most effective at removing PFAS (95-99%). NSF P473-certified solid carbon block filters also provide meaningful reduction. Granular pitcher filters are not recommended as a primary PFAS mitigation strategy.

Does the DWI improvement notice mean London water is unsafe?

No. A DWI improvement notice requires a company to take corrective action but does not mean the water is immediately unsafe. Current PFAS levels are below UK legal limits. The notice is a precautionary regulatory tool.

Thames Water PFAS: What the Enforcement Notice Means for You

Thames Water has active Drinking Water Inspectorate (DWI) improvement notices related to PFAS (per- and polyfluoroalkyl substances) at several of its water treatment works that draw from the River Thames and its catchment. This is the most significant outstanding water quality compliance issue for Thames Water customers in Greater London and the Thames Valley.

What are PFAS?

PFAS are a large group of man-made chemicals — over 4,000 compounds — used since the 1940s in products including non-stick cookware, firefighting foam (AFFF), food packaging, stain-resistant fabrics, and industrial processes. They are called "forever chemicals" because they do not break down naturally in the environment. PFAS accumulate in water sources and in the human body over time.

The main PFAS detected in UK water supplies are PFOA, PFOS, PFHxS, PFNA, and PFBS. Some are classified as potentially carcinogenic, endocrine-disrupting, or immunotoxic at higher exposure levels. Current regulatory science is evolving rapidly.

What the DWI improvement notices mean

A DWI improvement notice is a formal regulatory instrument issued when monitoring shows a parameter exceeding the DWI's investigatory level (IL) — which for total PFAS sum is currently 0.1 µg/l (100 ng/l). The IL is not a legal limit; it is a trigger for investigation and remedial action.

The improvement notices on Thames Water require it to install additional treatment — primarily granular activated carbon (GAC) filtration or reverse osmosis — at the affected works within specified timescales. Thames Water has committed to a major PFAS treatment investment programme through 2030.

Are PFAS levels in London water currently dangerous?

Current PFAS concentrations in London tap water are below UK legal limits — though the UK does not yet have statutory legal limits specifically for PFAS in drinking water (unlike the EU, which introduced a 0.1 µg/l sum PFAS limit in 2021). The DWI IL (also 0.1 µg/l) is based on precautionary health guidance from the Committee on Toxicity (COT).

The health risk at current UK tap water PFAS levels for healthy adults is assessed as low. The main at-risk groups are: pregnant women, breastfeeding mothers, infants, and those with compromised immune systems. For these groups, the precautionary principle suggests considering PFAS reduction.

What removes PFAS from tap water?

The two most effective domestic options are:

Reverse osmosis (RO): NSF/ANSI 58-certified systems remove 95–99% of PFAS. This is the gold standard for PFAS removal at home.
Activated carbon block filters: NSF/ANSI 53-certified solid block carbon filters (not granular) remove a significant portion of PFAS. Less complete than RO but much cheaper. Look for the NSF P473 certification specifically for PFAS reduction.

Pitcher filters using granular activated carbon (GAC) provide limited PFAS reduction and are not recommended as the primary PFAS mitigation strategy.

Enter your postcode to check whether your specific supply zone is under a PFAS improvement notice and see your zone's PFAS data.