Uxbridge Water Hardness & Quality Report (2026)

Uxbridge, in the London Borough of Hillingdon at the outer west London–Colne valley junction, is supplied by Thames Water from the River Thames storage reservoir system and Colne Valley reservoir complex. The Colne valley between Uxbridge and the Thames is occupied by a chain of large gravel pit reservoirs — including Wraysbury, Staines, Reservoirs Queen Mary, and King George VI — which store Thames-derived water before treatment and distribution. Thames Water's Kempton Park and Walton treatment works service the west London network. The Thames supply carries dissolved calcium from chalk-stream tributaries — the Kennet, Wey, and Mole — and from the Cotswold limestone upper Thames, contributing consistent hardness through the Thames gravel terrace storage and treatment.

Uxbridge's hardness of 240 mg/L (16.8°Clark) is consistent with the Thames chalk supply chemistry in the outer west London Colne valley zone. The Thames at west London carries accumulated chalk-derived calcium from the Chilterns and North and South Downs chalk-stream tributaries, and this chalk chemistry is preserved through reservoir storage and treatment. Uxbridge, being in the Colne valley directly between major Thames Water reservoir infrastructure, receives a concentrated Thames supply. The Drinking Water Inspectorate (DWI) classifies this supply as hard.

Limescale is a persistent household challenge in Uxbridge. At 240 mg/L, limescale forms in kettles within two to three weeks and fortnightly or monthly descaling is advisable. Combi-boiler heat exchangers accumulate deposits steadily — annual boiler servicing and fitting an in-line scale inhibitor are strongly recommended. Showerheads, taps, and shower screens develop regular deposits. Washing-up liquid lathers poorly. Using Calgon monthly in the washing machine and maintaining a regular descaling routine is important limescale management for Uxbridge households.