Catford Water Hardness & Quality Report (2026)

Catford, in the London Borough of Lewisham in south-east London, is supplied by Thames Water from the River Thames storage reservoir system at Hampton, Walton-on-Thames, and Staines, supplemented by North Downs Chalk Aquifer groundwater from chalk boreholes in the Surrey and Kent chalk country south of London. The outer south-east London supply zone at Catford receives Thames reservoir supply with strong chalk groundwater blending from the North Downs chalk — the Cretaceous Upper Chalk of the Surrey and north Kent North Downs — giving Catford's supply a high dissolved calcium content characteristic of the south-east London Thames Water distribution zone. Catford's hardness is consistent with adjacent south-east London zones including Beckenham (249.5 mg/L) and further east in the very hard Thames Water south-east London network.

Catford's very hard water — 280 mg/L (19.6°Clark) — reflects the strong North Downs Chalk groundwater blending in Thames Water's outer south-east London supply zone. The TDS of 753.6 mg/L confirms the high mineral content. The Drinking Water Inspectorate (DWI) classifies this supply as very hard.

Limescale is a very serious daily challenge in Catford. At 280 mg/L, thick limescale forms in kettles within one to two weeks requiring fortnightly descaling. Combi-boiler heat exchangers face serious limescale accumulation — annual boiler servicing with limescale inspection and a polyphosphate scale inhibitor are essential. Showerheads, taps, and shower screens develop heavy deposits. Washing-up liquid lathers very poorly. Catford homeowners should strongly consider a whole-house water softener for effective protection against North Downs chalk limescale damage in the south-east London supply zone.