Caterham Water Hardness & Quality Report (2026)

South East Water supplies Caterham in Surrey, drawing from deep boreholes sunk into the North Downs Chalk aquifer and from blended surface water sources. The North Downs form a prominent chalk escarpment running east–west through Surrey, and Caterham sits at the crest of this escarpment, directly above the aquifer. Key boreholes in the area access thick sections of the Upper Cretaceous Chalk at Kenley and Merstham, with water treated at Kenley and Redhill treatment works. At 283.5 mg/L (19.9°Clark), Caterham's water is very hard, reflecting the dominance of chalk groundwater in the local supply.

The North Downs Chalk at Caterham comprises steeply dipping Turonian and Cenomanian chalk beds that crop out at the surface of the escarpment. Groundwater here has long residence times within the aquifer, percolating through hundreds of metres of porous chalk and dissolving calcium carbonate extensively via the carbonic acid mechanism. Boreholes on the dip slope and crest of the North Downs yield water with very high calcium hardness — a defining characteristic of Surrey's water supply across the chalk outcrop zone.

Limescale management is a significant daily task in Caterham households. Kettles require descaling fortnightly — or more frequently for households with heavy use — to prevent element damage and calcium particles in drinks. The combi-boiler is at real risk without a properly fitted scale inhibitor and annual maintenance, given the sustained calcium load. Washing-up liquid does not lather freely in this very hard water; considerably more product is needed per wash than in softer areas. Taps, shower screens, and mixer heads develop heavy limescale deposits quickly; a twice-weekly wipe with a proprietary descaler or white vinegar is advisable, and a whole-house water softener is strongly recommended for long-term protection.