Does London water have PFAS?

Thames Water has active DWI PFAS improvement notices and is investing in GAC treatment. PFAS levels are below current UK legal limits. Those who prefer precaution can use an NSF/ANSI 58-certified reverse osmosis filter.

Why is London water so hard?

London water is hard because the Thames catchment draws from chalk and limestone aquifers in the Chilterns and North Downs. Calcium and magnesium carbonate dissolve naturally into the water. Hardness ranges from 250 to 350 mg/l as CaCO3.

Is it worth filtering London tap water?

For healthy adults, London tap water is safe unfiltered. You may choose to filter for limescale reduction (scale inhibitor or RO) or PFAS removal (RO or solid block carbon with NSF 58 certification). See our filter guide for recommendations.

Is London Tap Water Safe to Drink? 2026 Guide

Q: Is London tap water safe to drink?

Yes. London tap water meets all UK legal standards. Thames Water achieves DWI compliance. The main concerns for London water are very high hardness (250-350 mg/l) and PFAS improvement notices, but the water is safe for healthy adults.

London tap water is safe to drink and meets all UK legal drinking water standards. Thames Water, which supplies approximately 9.5 million customers across Greater London, the Thames Valley, and surrounding areas, is the UK's largest water company. Despite its well-publicised financial difficulties, the quality of water at the tap consistently meets Drinking Water Inspectorate (DWI) compliance standards.

PFAS: the key concern for London

The most significant water quality issue affecting London is PFAS (per- and polyfluoroalkyl substances, also known as forever chemicals). Thames Water has active DWI improvement notices related to PFAS treatment at several of its treatment works that draw water from the River Thames and its catchment.

The DWI issued improvement notices following the detection of PFAS compounds at concentrations above the DWI's voluntary investigatory level (0.1 µg/l total PFAS sum). Thames Water is investing in granular activated carbon (GAC) treatment to reduce PFAS levels. In the meantime, PFAS concentrations in London tap water are below the UK's current legal limits — though those limits are being reviewed. See: Thames Water PFAS explainer.

London has very hard water

London water is classified as very hard — typically 250 to 350 mg/l as CaCO3, depending on the zone. This is because the Thames catchment draws from chalk and limestone aquifers in the Chilterns and North Downs, which are rich in calcium and magnesium carbonate. Hard water is not a health risk, but it causes significant limescale accumulation on appliances, kettles, and heating systems.

A descaling filter (such as a magnetic conditioner or scale-inhibiting filter) can reduce limescale. Reverse osmosis removes hardness minerals entirely but produces wastewater in the process. See: London hard water guide.

Lead pipes in London

London has a significant legacy of lead service pipes, particularly in Victorian and Edwardian properties across inner London boroughs. Thames Water has been replacing lead pipes under its Proactive Lead Programme, but progress has been slow relative to the scale of the problem. If you live in a pre-1970 property, particularly in inner London, request a lead test from Thames Water. Hard water slightly reduces lead dissolution risk compared to soft water areas.

Is London tap water safe for babies?

London tap water is considered safe for making up infant formula. NHS guidance is to boil fresh tap water and allow it to cool before using — this kills bacteria. The main concern with London water for babies is not lead or PFAS but the high mineral content, which is safe at the levels present in London's supply. See: UK tap water safety for babies.