Sidcup Water Hardness & Quality Report (2026)

Thames Water supplies Sidcup, the south-east London suburb in the London Borough of Bexley — a well-established residential community with a mainline railway station, a busy high street, and a strong community identity at the junction of the Bexley and Bromley boroughs — from the River Lee chalk-tributary supply in the Thames Water south-east London distribution zone, treated at the Lee Valley Water Treatment Works complex. At 275 mg/L (19.3°Clark), Sidcup's water is very hard — consistent with the Thames Water Lee Valley chalk-dominant supply that delivers persistently very hard water throughout the south-east London Bexley and Bromley distribution corridor.

Sidcup lies in the Thames Water south-east London distribution zone where the Lee Valley chalk delivers mineralised chalk groundwater from Hertfordshire Chalk catchments via the Lee Valley reservoir chain. The Lee Valley chalk supply produces 275 mg/L with TDS 725.4 mg/L at Sidcup — very hard water with a TDS/hardness ratio (2.64) consistent with the south-east London Lee Valley chalk distribution tier at Belvedere (275 mg/L), Welling, and Eltham in the same Thames Water Bexley distribution zone.

At 275 mg/L, limescale is a persistent and significant household problem in Sidcup. Kettles should be descaled every two to three weeks. The combi-boiler needs a fitted scale inhibitor and annual professional servicing. Washing-up liquid requires generous quantities for adequate lather. Taps and shower heads develop substantial white chalk deposits within a week to ten days; a fortnightly descaling with white vinegar or a proprietary product keeps fittings in good condition. The very hard south-east London Lee Valley chalk supply at Sidcup is a permanent domestic feature of this established Bexley suburb — as consistent as the mainline service to London Bridge, and requiring the same regular attention.