Water hardness in Westminster (Greater London): 27.3°fH, quality index 5/10. Official UK data.
✓ Compliant with DWI standardsWestminster has hard water (27.3°fH). Weekly descaling is recommended. A water softener becomes worthwhile above 30°fH.
UK tap water is subject to the Water Supply (Water Quality) Regulations 2018, overseen by the Drinking Water Inspectorate (DWI). The sanitary compliance indicator shows whether the latest official analyses found any non-conformities on parameters such as bacteriology, nitrates, pesticides or heavy metals.
The TH (Total Hardness) measures calcium and magnesium content. Below 10°fH: soft. From 10 to 20: moderately soft. From 20 to 27: slightly hard. From 27 to 35: hard. Above 35: very hard. Westminster's water is hard at 27.3°fH.
Maintenance budget: ~£76/year
For 2 persons, water at 27.3°f deposits around 1.3 kg of limescale per year in your appliances. Estimated cost in descalers, salt and filters.
Calcium: ~44 mg per litre
Your water provides 44 mg of calcium/L, which is 4% of the recommended daily intake.
Filter jug: cartridge every 4 months
At 27.3°f, replace the cartridge every 4 months. An under-sink filter lasts 6 to 12 months.
The tap water hardness in Westminster is 27.3°fH, corresponding to hard water. In comparison, the England average in our dataset is 18.1°fH and the Greater London region average is 27°fH.
Yes. The water in Westminster meets DWI sanitary standards (Water Supply (Water Quality) Regulations 2018). The hardness of 27.3°fH affects taste and appliance maintenance, not safety. Water in Westminster is supplied and monitored by Thames Water.
At 27.3°fH, a water softener is optional in Westminster. Regular descaling (every 1 to 3 months depending on appliance) and a pitcher filter are sufficient to limit limescale buildup.
A hardness of 27.3°fH corresponds to approximately 44 mg of calcium per litre, or 4% of the recommended daily intake. This calcium is not dangerous; hard water can even contribute to your daily calcium intake.
Water in Westminster is supplied by Thames Water. Data source: Thames Water 2025.
Data: Thames Water official zone-level hardness reports (2025). Values verified via DWI drinking water quality database.