Durham Water Hardness & Quality Report (2026)

Durham, the cathedral city on the River Wear in County Durham, is supplied by Northumbrian Water from the River Wear catchment and the Kielder Transfer Scheme. The Wear rises in the North Pennines above Weardale — draining the Carboniferous Limestone and Millstone Grit of the upper Pennines — and flows east through Durham before entering the Magnesian Limestone country of east Durham. Northumbrian Water abstracts from the Wear at Burnhope Reservoir and other upper Weardale sources, treated at Wear Valley Water Treatment Works. The upper Wear supply is moderately soft from the Pennine limestone, while the Kielder Transfer contributes very soft Lake District and Tyne Valley water. Durham's position upstream of the eastern Magnesian Limestone plateau means the supply does not strongly reflect the hard limestone groundwater of coastal east Durham.

Durham's hardness of 139.5 mg/L (9.8°Clark) reflects the blend of North Pennine limestone and Kielder soft supply in the Wear valley distribution zone. The Carboniferous Limestone of the upper Weardale contributes moderate calcium to the Northumbrian Water blend. The Drinking Water Inspectorate (DWI) classifies this supply as moderately soft.

Limescale is a moderate concern in Durham. At 139.5 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 Durham households on the Wear valley supply.