Egham Water Hardness & Quality Report (2026)

Egham, the Surrey town on the south bank of the Thames at Runnymede — the meadow where Magna Carta was sealed in 1215 — is served by Thames Water. Supply to the Runnymede and Egham area draws on two sources: direct abstraction from the River Thames treated at Walton-on-Thames Water Treatment Works and the adjacent Wraysbury Reservoir complex, and chalk groundwater from boreholes in the Surrey and Berkshire Chalk Aquifer beneath the Thames valley. The Thames at Egham is fed by chalk-rich tributaries from the North Downs and the Berkshire chalk, and the river itself carries dissolved calcium bicarbonate from its upland chalk recharge areas. The moderate TDS of 548.5 mg/L and hardness of 223 mg/L are consistent with a Thames valley blend moderately diluted by Thames surface water compared with deeper confined chalk zones.

The Cretaceous Chalk beneath the Thames valley at Egham and Staines dips below the Eocene Reading and London Clay formations, but chalk springs and the chalk-fed character of the upper Thames headwaters deliver consistent calcium carbonate hardness to the river supply. Thames Water's treatment at Walton processes a blend of river and chalk groundwater that reliably produces hardness of 220–230 mg/L in the inner Thames valley distribution zone. The Wraysbury gravel pits, now flooded reservoirs adjacent to Egham, also contribute Thames-valley groundwater with chalk mineral character through the distribution network.

At 223 mg/L Egham's water is hard and limescale builds up steadily on exposed surfaces. Kettles should be descaled monthly using a citric acid tablet or diluted white vinegar. Shower heads and tap aerators accumulate mineral deposits over weeks and benefit from a monthly soak. Washing-up liquid must be used liberally. Inline scale inhibitors fitted before combi-boilers and washing machines reduce the risk of element damage. Egham's Thames-side character and proximity to the Wraysbury reservoirs makes it one of the more landmark-laden supply zones in Thames Water's network, even if the water's hardness requires persistent management.