Horsham Water Hardness & Quality Report (2026)

Horsham, the West Sussex market town in the Low Weald north of the South Downs, is supplied by South East Water from the South Downs Chalk Aquifer. South East Water operates licensed chalk borehole abstractions on the chalk dip slope and scarp of the South Downs — the Cretaceous Upper Chalk that forms the South Downs ridge south of Horsham — and pipes this chalk groundwater north through the distribution network to Horsham and the Low Weald. Despite Horsham's position in the Weald clay country rather than on the chalk itself, South East Water's supply is predominantly chalk-derived from boreholes on the South Downs, delivering extremely hard chalk groundwater to the town. The supply TDS of 953.5 mg/L confirms the exceptional mineral content.

Horsham's extremely hard water — 325 mg/L (22.8°Clark) — reflects the South Downs Chalk Aquifer supply conveyed from the chalk scarp to the north Sussex Low Weald. The Cretaceous Upper Chalk of the South Downs between Midhurst and Haywards Heath is a highly productive, pure chalk aquifer that yields very high dissolved calcium concentrations. The Drinking Water Inspectorate (DWI) classifies this supply as very hard, placing Horsham among the hardest water towns in England.

Limescale is an extremely serious daily challenge in Horsham. At 325 mg/L, very thick limescale forms in kettles within days and weekly descaling is necessary. Combi-boiler heat exchangers face extreme limescale risk — annual boiler servicing with a full limescale inspection and a polyphosphate scale inhibitor are non-negotiable. Showerheads, taps, and shower screens accumulate very heavy deposits extremely quickly. Washing-up liquid lathers virtually not at all. Horsham homeowners should strongly consider a whole-house water softener — it is a near-essential investment for protecting boilers, appliances, and plumbing on this South Downs chalk supply.