Cobham Water Hardness & Quality Report (2026)

Thames Water supplies Cobham in Surrey, a prosperous village in the Mole Valley where the River Mole runs northward toward the Thames at East Molesey. Supply is drawn from the River Thames abstracted at Walton-on-Thames, treated at Walton Water Treatment Works, and distributed via the Thames Water network across north Surrey. At 226 mg/L (15.9°Clark), Cobham's water is hard, reflecting the chalk-dominated Thames catchment and the North Downs Chalk aquifer influence that characterises all Thames Water supplies in the Surrey reaches.

The River Thames at Walton arrives having traversed the Chiltern Chalk and North Downs Chalk catchments, carrying sustained dissolved calcium bicarbonate from chalk springs and aquifer discharge throughout the middle Thames. The North Downs Chalk immediately south of Cobham seeps groundwater northward toward the Mole Valley and Thames, contributing chalk-derived hardness to the local distribution blend. The Walton Water Treatment Works processes this chalk-river abstraction and delivers it via the north Surrey network to Cobham and surrounding communities.

At 226 mg/L, limescale is a consistent household concern in Cobham. Kettles should be descaled monthly to maintain efficiency. The combi-boiler benefits from a fitted scale inhibitor to protect the heat exchanger, and annual servicing is recommended. Washing-up liquid requires more product than in softer-water areas to achieve a satisfactory lather. Taps and shower heads develop visible white limescale deposits within one to two weeks; a fortnightly wipe with white vinegar or a proprietary descaling solution keeps fittings clean and prevents hard-water staining from accumulating permanently on surfaces — standard domestic practice in this hard chalk-river Surrey supply zone.