58 postcode districts testedWater quality in London
According to TapWater.uk's analysis, London scores 8.3/10 for drinking water quality in 2026, based on data from 58 postcode districts. Water quality across Greater London, supplied primarily by Thames Water and Affinity Water.
8.3 / 10
58 areas tested · 1 supplier
Tap water in London has an average safety score of 8.3 out of 10 based on testing across 58 postcode districts. Water is supplied by Thames Water. The overall water quality is good. Data is sourced from the Environment Agency and water company testing via the Stream Water Data Portal.
Cities in London
Average water quality score by city.
276mg of limescale minerals in every litre, on average across London
London water is very hard
Hard starts at 180 mg/L, very hard at 250. Hardness varies by area; check your own postcode for the reading where you live.
Softener quotes in London
At 276 mg/L a softener protects the boiler, kettle and taps. Tell us your postcode and we will pass your request to installers who cover it. Free, no obligation.
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River health around London
None of the 12 rivers and waters that London drains into is rated good by the Environment Agency. All of them fail the chemical test, as every river in England does, because of long-lasting pollutants such as mercury and PFOS. This describes the rivers, not your tap water.
| River or water | Ecological health | Postcode districts |
|---|---|---|
| Thames Middle | Moderate | E1, E14, NW1, SE1, SE5, SE10, SE16, SE17 and 14 more |
| Dollis Brook and Upper Brent | Moderate | EN5, N2, N3, N20, NW3, NW4, NW8, NW11 |
| Lee (Tottenham Locks to Bow Locks/Three Mills Locks) | Moderate | E2, E3, E5, E8, E9, N16 |
| Thames Upper | Moderate | SW6, W6, W11, W12, W14 |
| Lower Brent | Moderate | NW6, W9, W10 |
| Marsh Dykes (Woolwich) | Moderate | SE2, SE18, SE28 |
| Quaggy | Moderate | SE3, SE7, SE9 |
| Pymmes Brook upstream Salmon Brook confluence | Moderate | EN4, N12 |
| Ravensbourne (Catford to Deptford) | Moderate | SE15, SE22 |
| Silk Stream and Edgware Brook | Moderate | HA8, NW7 |
| Moselle Brook | Moderate | NW5 |
| Pool River | Moderate | SE21 |
Environment Agency classification, 2025. River health across England
Areas to watch
Questions about London water
Is tap water safe in London?
Based on our analysis of 58 postcode districts in London, the average water quality score is 8.3/10, which is safe. Water is supplied by Thames Water.
Which area has the best water in London?
N2 (Barnet) has the highest water quality score in London at 8.8/10.
Which area has the worst water in London?
E2 (Tower Hamlets) has the lowest water quality score in London at 7.0/10. Check the postcode page for details on specific contaminants.
Is London water hard or soft?
Water in London has an average hardness of 276 mg/L CaCO₃, which is classified as very hard. Hardness varies by area — check your postcode for exact levels.
Who supplies water in London?
Water in London is supplied by Thames Water.
Data sourced from the Environment Agency Water Quality Archive and water company testing via the Stream Water Data Portal. See our methodology for how scores are calculated. Reviewed by the TapWater.uk research team.