Feltham Water Hardness & Quality Report (2026)

Feltham, in the London Borough of Hounslow in outer south-west London adjacent to Heathrow Airport, is supplied by Thames Water from the Thames storage reservoir system and the west London distribution network. Thames Water's west London supply draws from the Thames at Hampton and Walton-on-Thames, treating at Walton Water Treatment Works, with storage in the Kempton Park, Queen Mary, and Island Barn reservoir complexes. Feltham's supply distribution zone sits within the outer west London Thames reservoir supply corridor — the same supply network serving Hounslow and the Heathrow area — but at a network position where the Thames reservoir supply is somewhat less concentrated in chalk-derived calcium than the chalk groundwater-supplemented zones nearer Uxbridge and Hounslow town centre.

Feltham's hardness of 193 mg/L (13.5°Clark) reflects the Thames Valley supply chemistry in the outer west London Hounslow distribution network, at a zone where the Thames reservoir supply — carrying chalk-stream tributary calcium from the Kennet, Wey, and Mole — is the dominant hardness source without additional chalk groundwater supplementation. This is moderately lower than Hounslow town centre (309.5 mg/L) which has a stronger chalk groundwater component. The Drinking Water Inspectorate (DWI) classifies this supply as moderately hard.

Limescale is a regular household concern in Feltham. At 193 mg/L, limescale forms in kettles within three to four weeks and monthly descaling is advisable. Combi-boiler heat exchangers accumulate deposits steadily — annual servicing with a limescale check and fitting an in-line scale inhibitor are recommended. Showerheads, taps, and shower screens develop consistent deposits. Washing-up liquid lathers moderately. Using Calgon monthly in the washing machine and a regular descaling routine is appropriate limescale management for Feltham households.