Gerrards Cross Water Hardness & Quality Report (2026)

Affinity Water supplies Gerrards Cross in south Buckinghamshire via the Colne Valley supply zone. The town's water is drawn from a blend of groundwater from the Chiltern Chalk aquifer and the Colne Valley gravels, supplemented by surface water abstraction, treated at regional works serving south Buckinghamshire and the west London fringe. At 173 mg/L (12.1°Clark), Gerrards Cross experiences moderately hard water, slightly softer than peak Chiltern chalk hardness due to the blending influence of valley gravel groundwater and surface water components.

The Chiltern Chalk underpins the high ground to the north-west of Gerrards Cross, contributing calcium-rich groundwater to boreholes on the chalk dip slope. However, the Colne Valley gravels — Pleistocene terrace deposits of flint, sand, and gravel — also contain calcium derived from reworked chalk material, producing groundwater of moderate hardness. Blending these two sources, with their differing hardness profiles, moderates the final supply to values somewhat below the peak chalk hardness typical of the Chiltern crest zone further north.

At 173 mg/L, limescale accumulates at a moderate rate in Gerrards Cross homes. Descaling the kettle every four to six weeks is typically sufficient to keep the element clean and beverages free of calcium flakes. The combi-boiler benefits from a fitted scale inhibitor as standard precaution, with annual servicing recommended. Washing-up liquid works well at normal quantities, though slightly reduced lathering may be noticeable. Taps and shower heads accumulate visible limescale deposits over several weeks; a monthly wipe with white vinegar or a mild descaling solution is generally adequate to keep fittings in good condition and looking their best.