Tavistock Water Hardness & Quality Report (2026)

South West Water supplies Tavistock, the ancient stannary and market town on the western edge of Dartmoor in Devon — a historic tin-mining centre on the River Tavy, home of Sir Francis Drake and the Tavistock Canal, and a gateway to the wild Dartmoor moorland — from the west Devon supply network drawing on Devonian Limestone (Devonian reef limestone) and surface blend sources in the west Devon supply zone, treated at Crownhill Water Treatment Works near Plymouth. At 240.5 mg/L (16.9°Clark) and a TDS of 701 mg/L, Tavistock's water is hard — surprisingly so for a Dartmoor-edge community — reflecting the supply distribution from the Plymouth zone rather than from the naturally very soft Dartmoor granite moorland catchments that surround the town.

Tavistock borders Dartmoor — the acid Dartmoor Granite moorland that naturally produces very soft water — but South West Water supplies Tavistock from the Plymouth metropolitan distribution network, which draws on the Devonian Limestone reef-knoll geology of south Devon and Plymouth Sound catchment aquifer blend, producing significantly harder 240.5 mg/L with TDS 701 mg/L water than the adjacent Dartmoor granite moorland would naturally yield. The high TDS/hardness ratio (~2.9) also indicates elevated non-carbonate minerals — possibly sulphate from historic copper and tin mining mineral spoil in the Tamar Valley.

At 240.5 mg/L, limescale is a persistent household challenge in Tavistock. Kettles should be descaled monthly. The combi-boiler benefits from a fitted scale inhibitor and annual professional servicing. Washing-up liquid requires more product per wash. Taps and shower heads develop visible white limescale deposits within one to two weeks; a fortnightly wipe with white vinegar or a proprietary descaling product keeps fittings clean. The unexpectedly hard supply at Tavistock is a reminder that proximity to the soft Dartmoor granite moorland does not guarantee soft tap water when the town is supplied from the harder Plymouth distribution network.