Redruth Water Hardness & Quality Report (2026)

Redruth, in central Cornwall in the historic tin and copper mining district of Gwennap, is supplied by South West Water from Stithians Reservoir on the Carnon River south of Redruth and the broader west Cornwall supply network. Stithians Reservoir impounds the Carnon River — a river draining the Devonian Mylor Slate and Falmouth Beds metasedimentary rocks of the Carnon valley, ancient marine sediments metamorphosed by Variscan granite intrusion. South West Water distributes from Stithians and supplements from the wider west Cornwall network, which includes supply from Drift Reservoir near Penzance and the Loe Pool system. Redruth's somewhat elevated hardness for a Cornish town reflects the Devonian metasedimentary catchment of Stithians — calcite-bearing slate and phyllite bands in the Mylor Slate leach moderate calcium, in contrast to the almost calcium-free granite bosses of west Cornwall.

Redruth's hardness of 141 mg/L (9.9°Clark) is notably elevated compared to the much softer granite-dominated west Cornwall supply zones, reflecting the Devonian Mylor Slate and metasedimentary catchment of the Carnon River, where carbonate-bearing metamorphic rocks dissolve moderate calcium. The Drinking Water Inspectorate (DWI) classifies this supply as moderately soft.

Limescale is a moderate concern in Redruth, higher than might be expected for Cornwall. At 141 mg/L, limescale forms gradually and kettles need descaling every one to two months. Combi-boiler heat exchangers accumulate modest deposits; annual servicing is sensible. Showerheads and taps develop light deposits. Washing-up liquid lathers reasonably well. A monthly Calgon tablet in the washing machine and a regular kettle descale is adequate limescale management for Redruth households.