Exeter Water Hardness & Quality Report (2026)

Exeter's water supply is managed by South West Water, drawing from the Dartmoor and east Devon upland reservoir system. Primary sources include Kennick Reservoir, Tottiford Reservoir, and Trenchford Reservoir — three linked impoundments on the headwaters of the Teign system in Dartmoor National Park — supplemented by Stafford Moor Reservoir on the west Dartmoor fringe and contributions from the River Exe catchment in Devon. Water is treated at South West Water's facilities in Devon before distribution to Exeter and the surrounding area. The Dartmoor reservoir system, constructed between the 1870s and 1960s, supplies not only Exeter but a substantial portion of eastern and central Devon from its high moorland catchment.

Exeter's very soft water — 55 mg/L (3.9°Clark) — is a consequence of the Dartmoor granite and Devonian metamorphic geology of its upland catchments. The Kennick and Teign headwater reservoirs sit within the eastern Dartmoor National Park, underlain by Variscan granite — an igneous rock formed approximately 300 million years ago, highly resistant to chemical weathering and releasing negligible calcium or magnesium into draining water. The surrounding Devonian slates and phyllites are similarly impervious. Rainfall running off these moorland surfaces and granite tors carries almost no dissolved minerals before entering the reservoirs. The result is water classified as soft by the Drinking Water Inspectorate (DWI).

Limescale is rarely a practical concern for Exeter residents. At 55 mg/L, limescale accumulates very slowly — kettles typically need descaling only once or twice a year, and deposits on taps, showerheads, and combi-boiler components are minimal. Combi-boilers face negligible limescale stress, helping maintain boiler efficiency throughout the appliance's life. Washing-up liquid lathers generously. The Dartmoor supply gives Exeter some of the softest water of any city in south England. The main consideration for Exeter households, as with all soft-water cities, is that soft, slightly acidic water can be mildly corrosive to older metal pipework — running the kitchen tap briefly before drinking is a sensible habit in older properties.