Yarm Water Hardness & Quality Report (2026)

Northumbrian Water supplies Yarm, a historic market town on a loop of the River Tees in Stockton-on-Tees. Water reaching Yarm is drawn from a combination of Tees Valley upland reservoirs — including Cow Green and Selset in the North Pennines — and groundwater from the Magnesian Limestone aquifer of County Durham, treated at Broken Scar Water Treatment Works on the Tees near Darlington before distribution across the Tees Valley. At 193 mg/L (13.5°Clark), Yarm's water is moderately hard — notably harder than typical North East reservoir supply, driven by the Permian Magnesian Limestone geology underlying this part of the Tees lowlands.

The Magnesian Limestone (Permian Zechstein) forms a continuous belt running north–south through County Durham and extending southward into the Tees plain. Groundwater abstracted from this formation has dissolved significant quantities of calcium and magnesium carbonate over long residence times, producing water with moderate to high hardness. The Tees Valley reservoir supply — sourced from acidic North Pennine moorlands — is softer, but blending with Magnesian Limestone groundwater raises the overall hardness in the Tees lowland distribution zone to moderately hard levels at Yarm.

Limescale is a noticeable domestic concern in Yarm. Kettles benefit from descaling every four to six weeks to prevent element efficiency loss. The combi-boiler should be fitted with a scale inhibitor and serviced annually. Washing-up liquid performs adequately at normal quantities. Taps and shower heads develop moderate limescale deposits over several weeks; a monthly wipe with white vinegar or a mild descaling product is recommended to keep fittings clean and prevent hard-water staining. The hardness level is higher than in most North East towns due to the Magnesian Limestone influence in this part of the Tees catchment.