Hanworth Water Hardness & Quality Report (2026)

Hanworth, the outer west London neighbourhood in the London Borough of Hounslow between Feltham, Twickenham and the Bushy Park fringe, is supplied by Thames Water from a blend of Thames river-abstraction treated at Hampton Water Treatment Works and chalk borehole groundwater from the Thames valley and Colne valley supply system. Hanworth's hardness at 223 mg/L positions it between the very Thames-surface-water-dominant New Malden (187 mg/L) to the east and the chalk-borehole-dominant Isleworth (282 mg/L) to the north — reflecting an intermediate blend proportion with a moderate chalk borehole component supplementing the Hampton Thames treatment. The TDS of 542 mg/L (ratio 2.43) is moderately elevated, confirming a blend with meaningful chalk borehole input but less than the extreme chalk-dominant zones of outer west London. Thames Water distributes from multiple supply sources into the outer west London network, and Hanworth's supply zone sits in the moderate-chalk-blend tier between the softer Hampton-dominated zones and the very hard chalk borehole zones of Northolt (303.5 mg/L) and Ruislip (315.5 mg/L) further north-west.

The River Thames at Hampton carries chalk-influenced water from the upper Thames chalk catchment at 180–200 mg/L. Chalk Aquifer borehole groundwater from the Thames valley and Colne valley contributes concentrated chalk water at 290–310 mg/L to the blend. In Hanworth's distribution zone, the blend ratio produces 223 mg/L — harder than the Thames-surface-water-dominant zones of Kingston and Wimbledon but softer than the chalk-borehole-dominant outer west London supply areas. The TDS of 542 mg/L reflects this chalk/Thames-surface-water hybrid character.

At 223 mg/L Hanworth's water is hard and limescale management is a regular domestic routine. Kettles benefit from monthly descaling with a citric acid tablet. Shower screens develop a calcium haze requiring regular white vinegar treatment. Washing-up liquid must be used generously. Combi-boilers benefit from inline scale inhibitor protection. Hanworth's outer west London suburban character — playing fields, low-density housing and the proximity to Feltham and the Bushy Park estate — is combined with a hard Thames/chalk blend water supply typical of the Thames Water outer west distribution zone.