Sunbury-on-Thames Water Hardness & Quality Report (2026)

Sunbury-on-Thames, the Surrey town on the south bank of the Thames between Walton-on-Thames and Hampton in the Spelthorne area, is served by Thames Water. Supply here draws primarily on direct abstraction from the River Thames treated at the nearby Hampton Water Treatment Works — one of the largest water treatment facilities in Europe — which processes vast quantities of Thames river water daily. The Thames at Hampton carries water derived from its chalk-influenced upper catchment in the Chilterns and Berkshire Downs, but the dominant treatment and dilution at Hampton tempers the chalk hardness considerably compared with zones relying on deep chalk boreholes. The moderate TDS of 415.2 mg/L reflects the predominantly surface-water character of this supply, with limited deep chalk groundwater blending in the Sunbury distribution zone.

The River Thames at Hampton carries calcium bicarbonate acquired from chalk and limestone in its upper catchment — the Chiltern Hills, the Berkshire chalk and the Cotswold Jurassic limestone of the upper Thame and Cherwell. By the time this water reaches Hampton, it has been diluted by non-chalk tributaries and mixed with River Mole and River Wey inputs of varying hardness. Thames Water's Hampton treatment processes this mixed-character river water, typically producing supply at 180–200 mg/L hardness — notably softer than the deep chalk borehole-dominated supply zones of outer south-west London such as Windsor or Ruislip.

At 186.5 mg/L Sunbury-on-Thames has moderately hard water and limescale is a manageable rather than severe household concern. Kettles benefit from descaling every four to six weeks using a citric acid tablet or white vinegar. Shower screens show gradual limescale spotting and should be cleaned monthly. Washing-up liquid lathers adequately with moderate amounts. Combi-boilers and white goods appliances would benefit from inline scale inhibitors but are not at extreme risk. Sunbury's Thames-side riverside character and proximity to the Hampton treatment works reflect the town's intimate relationship with the river that also defines the mineral character of its tap water.