Bodmin Water Hardness & Quality Report (2026)

South West Water supplies Bodmin, the county town of Cornwall on the south-western edge of Bodmin Moor. Supply is drawn from Colliford Lake — Cornwall's largest reservoir, impounded on the River Fowey on the Bodmin Moor granite — and from Porth Reservoir and regional Cornwall sources, treated at Colliford and regional Cornwall works before distribution across mid-Cornwall. At 155.5 mg/L (10.9°Clark), Bodmin's water is moderately soft — notably harder than most of Cornwall — reflecting a supply blend where soft Bodmin Moor granite water is mixed with water drawn from the Carboniferous Limestone and Devonian limestone outcrops fringing the moor.

Colliford Lake on Bodmin Moor sits directly on the Cornubian Granite batholith — one of the most chemically inert rock formations in Britain — producing naturally very soft, slightly acidic water with negligible calcium content. However, Bodmin's supply incorporates water from catchments and groundwater sources in the limestone country bordering the granite, particularly from Devonian limestone and calcareous reef-knoll formations in the south Cornish landscape north and east of Bodmin. These limestone contributions substantially elevate hardness in the blended supply above the very soft granite baseline.

At 155.5 mg/L, Bodmin's water is moderately soft and limescale demands are noticeable but manageable. Descaling the kettle every six to eight weeks is typically adequate. The combi-boiler benefits from a fitted scale inhibitor as a precaution. Washing-up liquid lathers satisfactorily at everyday quantities. Taps and shower heads develop moderate limescale deposits over a few weeks; a monthly wipe with white vinegar or a mild descaler keeps fixtures clean. Bodmin's water is harder than the soft granite-fed supplies of west Cornwall, reflecting the geological complexity of mid-Cornwall at the limestone–granite boundary.