Staines Water Hardness & Quality Report (2026)

Staines-upon-Thames, the Surrey town in the Borough of Spelthorne at the Thames reservoir complex, is supplied by Thames Water from the Staines and King George VI Reservoirs — the large open reservoirs immediately adjacent to the town north of the Thames. Thames Water abstracts from the River Thames and stores in the west London reservoir complex, treating at Walton Water Treatment Works and Queen Mary Reservoir treatment facilities. The Staines reservoirs serve as key balancing storage for the west London supply. The Thames supply at Staines carries dissolved calcium from chalk-stream tributaries — particularly the River Colne (draining the Chiltern chalk) and the Wey and Mole (draining the North and South Downs chalk) — producing moderately hard water characteristic of the Thames Valley at the west London reservoir intakes.

Staines's hardness of 215.5 mg/L (15.1°Clark) reflects the Thames supply chemistry at the west London reservoir complex — chalk-stream tributary calcium accumulated along the Thames's south-east England course. The Thames at the west London intakes carries contributions from the Chiltern chalk drainage via the Colne and Chess, and from the North Downs drainage via the Mole and Wey, producing consistent moderate hardness. The Drinking Water Inspectorate (DWI) classifies this supply as hard.

Limescale is a persistent household challenge in Staines. At 215.5 mg/L, limescale forms in kettles within two to three weeks and monthly descaling is advisable. Combi-boiler heat exchangers accumulate deposits steadily — annual boiler servicing and an in-line scale inhibitor are 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 Staines households on the Thames Valley reservoir supply.