Marlow Water Hardness & Quality Report (2026)

Thames Water supplies Marlow, a picturesque Thames-side market town in Buckinghamshire on the outer edge of the Chilterns. Supply is drawn from the River Thames abstracted at Medmenham upstream of Marlow and from Chiltern Chalk aquifer boreholes in the Thames Valley, treated at Medmenham Water Treatment Works before distribution across the Marlow and Chiltern supply zone. At 242.5 mg/L (17.0°Clark), Marlow's water is hard, reflecting the profound influence of the Chiltern Chalk catchment through which the Thames flows from its source in the Cotswold limestone country down through the chalk downland of Berkshire and the Chilterns.

The River Thames at Marlow drains the Chiltern Chalk escarpment and dip slope, receiving substantial chalk spring and groundwater inputs from the Chiltern Chalk aquifer throughout its middle course. The chalk springs feeding the Thames above Marlow carry classic calcium bicarbonate hardness accumulated over long underground residence times in the porous Cretaceous chalk. The Thames Valley Chalk directly beneath Marlow contributes further groundwater of comparable composition, producing the consistently hard supply that characterises communities along the chalk Thames corridor.

Limescale is a persistent household concern in Marlow. Kettles should be descaled monthly to maintain efficiency and avoid chalky deposits in drinks. The combi-boiler benefits from a fitted scale inhibitor to protect the heat exchanger, and annual servicing is recommended. Washing-up liquid requires slightly more product than in softer areas to achieve a 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 and prevents hard-water staining from becoming permanent — a small but routine part of domestic upkeep in this quintessentially hard chalk-river town.