Leatherhead Water Hardness & Quality Report (2026)

Leatherhead, in the Mole Valley district of Surrey where the River Mole cuts through the North Downs in the famous Mole Gap, is supplied by South East Water from the North Downs Chalk Aquifer via chalk boreholes in the Mole valley and chalk downs of Surrey. The Mole Gap is a wind gap through the chalk ridge of the North Downs where the Mole crosses the chalk — the chalk aquifer is exposed at the surface in the valley sides, and South East Water draws from productive chalk boreholes in the chalk of the Leatherhead and Mickleham area. The Cretaceous Upper Chalk of the Mole valley is very productive and produces high dissolved calcium groundwater typical of the Surrey North Downs. South East Water treats and distributes to Leatherhead and the Mole valley from the chalk supply.

Leatherhead's hard water — 217 mg/L (15.2°Clark) — reflects the North Downs Chalk Aquifer at the Mole Gap, where the chalk is particularly accessible and productive. The Drinking Water Inspectorate (DWI) classifies this supply as hard.

Limescale is a persistent household challenge in Leatherhead. At 217 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 Leatherhead households on the North Downs chalk supply.