Slough Water Hardness & Quality Report (2026)

Slough, a unitary authority town in Berkshire in the Thames Valley corridor, is supplied by Thames Water. The town is served by a blend of River Thames surface water stored in the Queen Mother Reservoir near Datchet and Wraysbury Reservoir — both large off-river storage facilities in the Thames Valley — and groundwater abstracted from Thames Valley Chalk Aquifer boreholes. The chalk here underlies the eastern Berkshire and Buckinghamshire Chilterns and their dip slope extending into the Thames Valley. Water is treated at Kempton Park Water Treatment Works and Farmoor Water Treatment Works near Oxford, before distribution through the western Thames Water network to Slough and east Berkshire. Slough's position adjacent to Heathrow and on the main Thames Valley supply axis means it shares infrastructure with a large swath of London's western suburbs.

Slough's hardness of 238 mg/L (16.7°Clark) reflects the chalk geology of the Thames Valley. The Chiltern Hills to the north and east of Slough are formed from Cretaceous Upper Chalk — a highly permeable, calcium-rich limestone. The River Thames at the point of abstraction near Staines has traversed extensive chalk catchments across the Berkshire Downs, Chilterns, and Cotswold limestone country. Thames Valley chalk borehole water adds further very high calcium concentrations from direct groundwater-chalk contact. The blended supply is classified as hard by the Drinking Water Inspectorate (DWI).

Limescale is a familiar and persistent challenge in Slough homes. At 238 mg/L, limescale accumulates rapidly in kettles — a visible white layer forms within two to three weeks and fortnightly descaling is advisable. Combi-boiler heat exchangers face consistent limescale pressure, and annual boiler servicing with a limescale check is essential; an in-line scale inhibitor is strongly recommended for boiler protection. Showerheads and taps develop heavy limescale deposits, and washing-up liquid lathers poorly. Glass shower screens need regular attention with a proprietary limescale remover. Slough homeowners should consider a magnetic water conditioner or full water softener for long-term protection of heating systems and household appliances.