Helston Water Hardness & Quality Report (2026)

South West Water supplies Helston, the Cornish market town at the gateway to the Lizard Peninsula — a town famous for the Flora Dance (Helston Furry Dance) on 8 May each year, one of the oldest surviving folk festivals in England, and set in the ancient landscape of the Carnmenellis and Lizard Peninsulas — from Stithians Reservoir impounded on the Carnmenellis Granite upland south-west of Redruth, treated at Stithians Water Treatment Works. At 134 mg/L (9.4°Clark), Helston's water is slightly hard — notably harder than the granitic upland core communities — reflecting calcium contributions from the Serpentinite and Gabbro geology of the Lizard Peninsula that partially characterises the South West Water west Cornwall distribution zone.

Helston lies at the foot of the Carnmenellis Granite adjacent to the Lizard Peridotite Complex — Europe's largest surface exposure of mantle rock, an extraordinarily rare geology of serpentinite, gabbro, and hornblende-schist that weathers to release calcium and magnesium. Stithians Reservoir on the granite provides moderately soft supply, but the distribution zone blends water from the broader west Cornwall catchment where Lizard geology raises magnesium and calcium above the granite baseline. The result is 134 mg/L with TDS 310.3 mg/L — slightly hard, harder than other Cornish granitic zones.

At 134 mg/L, limescale is a moderate and manageable domestic concern in Helston. Descaling the kettle every six to eight weeks is typically adequate. The combi-boiler benefits from a standard scale inhibitor as a precaution. Washing-up liquid lathers adequately at everyday quantities. Taps and shower heads develop moderate deposits over several weeks; a monthly wipe with white vinegar keeps fixtures in good condition. The slightly hard supply at Helston is harder than much of Cornwall — a product of the unique and geologically extraordinary Lizard Peninsula that gives this part of the west Cornish supply zone its distinctive water chemistry.