Exmouth Water Hardness & Quality Report (2026)

Exmouth, in East Devon at the mouth of the River Exe on the Triassic Red Sandstone coast, is supplied by South West Water from the River Exe catchment and the Permo-Triassic New Red Sandstone aquifer of east Devon. The River Exe drains the Exmoor and Dartmoor upland fringes — relatively insoluble Devonian sandstone and moorland — but passes through the Permian and Triassic Red Sandstone country of the Exe valley and Exeter basin. South West Water draws from the Exe valley at Pynes near Exeter and from the Permo-Triassic sandstone aquifer beneath the east Devon coastal plain, where calcium-bearing minerals in the red sandstone cement produce moderately mineralised groundwater. The resulting supply is moderately soft — significantly softer than the Devonian limestone zones at Newton Abbot (252.5 mg/L) further south.

Exmouth's hardness of 138.5 mg/L (9.7°Clark) reflects the blend of River Exe upland catchment and Permo-Triassic Red Sandstone groundwater in South West Water's Exe estuary supply zone. The Drinking Water Inspectorate (DWI) classifies this supply as moderately soft.

Limescale is a moderate concern in Exmouth. At 138.5 mg/L, limescale forms gradually in kettles and descaling every one to two months is typically sufficient. 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 most Exmouth households.