Lewes Water Hardness & Quality Report (2026)

South East Water supplies Lewes, the county town of East Sussex on the River Ouse at the gap in the South Downs. Supply is drawn from the South Downs Chalk aquifer via boreholes in the Ouse Valley and from surface water abstraction on the chalk-stream River Ouse, treated at Lewes Water Treatment Works before distribution across the Ouse Valley and the East Sussex county town. At 227.5 mg/L (16.0°Clark), Lewes's water is hard, driven by the dominant chalk geology of the South Downs that rises spectacularly north and south of the town.

The River Ouse above Lewes drains the South Downs Chalk and the High Weald sandstone country, with the chalk contribution — via springs and chalk aquifer seeps — dominating the river's mineral character by the time it reaches Lewes. The town sits directly in the chalk gap through the South Downs, surrounded by the Upper Cretaceous Chalk on both sides. Borehole abstraction from the local chalk aquifer and the chalk-fed River Ouse together produce the consistently hard water that characterises the Lewes supply zone throughout the year.

At 227.5 mg/L, limescale is a consistent household challenge in Lewes. 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 areas to achieve satisfactory lather. Taps and shower heads develop visible white limescale within one to two weeks; a fortnightly wipe with white vinegar or a proprietary descaling solution keeps fittings clean. The hard chalk water is inseparable from the landscape around Lewes, where the white cliffs of the South Downs define both scenery and water quality.