Sanderstead Water Hardness & Quality Report (2026)

SES Water (Sutton and East Surrey Water) supplies Sanderstead, a residential suburb in the London Borough of Croydon on the North Downs chalk plateau — a leafy area of Edwardian and interwar houses perched on the chalk ridge at the highest point in Croydon, with the Selsdon Wood nature reserve nearby — from North Downs Chalk boreholes in the south Croydon chalk belt, treated at Mole Valley Water Treatment Works near Leatherhead. At 312.5 mg/L (21.9°Clark) and a TDS of 895.4 mg/L, Sanderstead's water is extremely hard — among the hardest in Greater London — consistent with the fully saturated North Downs Upper Chalk aquifer that delivers exceptional chalk mineralisation to the SES Water south Croydon supply zone.

Sanderstead sits directly on the North Downs Chalk at one of the highest points in south London, where the unconfined chalk aquifer is freely recharged and at maximum thickness. SES Water supplies this area from chalk boreholes drawing on the same highly mineralised Upper Chalk formation that supplies Ashtead (321 mg/L), Horley (273 mg/L), and the wider Surrey chalk belt — extracting 312.5 mg/L with TDS 895.4 mg/L groundwater that places Sanderstead firmly among the hardest public water supplies in London.

At 312.5 mg/L, limescale is an extreme and relentless household problem in Sanderstead. Kettles must be descaled weekly to prevent rapid element failure. The combi-boiler faces very high risk of premature breakdown without a properly fitted, annually replaced scale inhibitor and regular professional servicing. Washing-up liquid requires very generous quantities for any meaningful lather. Taps, shower heads, and basin fittings develop heavy chalk encrustation within days; a weekly descaling with white vinegar or a proprietary product is essential. A whole-house water softener is very strongly recommended for all Sanderstead households.