Compare tap water hardness in 5 cities in Greater London, England. Average: 27°fH (Average quality).
In Greater London, tap water hardness averages 27°fH, corresponding to hard water. The softest water is found in Croydon (28.1°fH, score 5/10) and the hardest in Westminster (27.3°fH, score 5/10). The England average in our dataset is 18.1°fH. All 5 cities have water compliant with DWI regulations (Water Supply (Water Quality) Regulations 2018).
The average tap water hardness in Greater London is 27°fH, corresponding to hard water. Among the 5 cities covered, the softest water is found in Croydon (28.1°fH) and the hardest in Westminster (27.3°fH). The England average in our dataset is 18.1°fH.
Yes. Tap water in Greater London is regulated by the Drinking Water Inspectorate (DWI) under the Water Supply (Water Quality) Regulations 2018. Water hardness of 27°fH does not affect safety; it only influences appliance maintenance and taste. All 5 cities in our database have compliant water.
With an average of 27°fH, a water softener or anti-scale filter is a worthwhile investment in Greater London. Limescale significantly shortens the lifespan of boilers, washing machines and kettles. A softener is particularly recommended in cities above 30°fH such as Westminster (27.3°fH).
Water in Greater London is supplied by Thames Water. Data in our database comes from official zone-level analyses published by these utilities (2025).
All 5 cities in Greater London with their hardness values are listed on this page. Click on any city name to get full details: quality index, DWI compliance, impact on appliances and personalised recommendations.
Data: Thames Water official zone-level hardness reports (2025). Readings verified via DWI drinking water quality database.