Eltham Water Hardness & Quality Report (2026)

Eltham, in the London Borough of Greenwich in south-east London, is supplied by Thames Water from the Thames storage reservoir system and North Downs Chalk Aquifer groundwater. Thames Water holds licensed borehole abstractions in the chalk country near Bromley and the north Kent fringe — the Cretaceous Upper Chalk accessible in the outer south-east London supply zone — supplemented by Thames reservoir supply from the west London network. Eltham's south-east London position, near the outer Bromley chalk fringe, gives the supply zone a higher chalk groundwater component than inner London areas, raising the hardness above the pure Thames reservoir baseline. The north Kent chalk and the chalk beneath the south-east London suburbs contribute significant dissolved calcium.

Eltham's hard water — 233 mg/L (16.3°Clark) — reflects the Thames supply enhanced by a significant North Downs Chalk Aquifer groundwater contribution in the outer south-east London supply zone. This is consistent with nearby Beckenham (279.5 mg/L) and South Croydon (235.5 mg/L), confirming the hard water characteristic of the outer south-east London chalk fringe distribution zones. The Drinking Water Inspectorate (DWI) classifies this supply as hard.

Limescale is a persistent household challenge in Eltham. At 233 mg/L, limescale forms in kettles within two to three weeks and monthly descaling is advisable. Combi-boiler heat exchangers accumulate deposits steadily — annual boiler servicing and an in-line scale inhibitor are recommended. Showerheads, taps, and shower screens develop regular deposits. Washing-up liquid lathers poorly. Using Calgon monthly in the washing machine and maintaining a regular descaling routine is important limescale management for Eltham households.