Bath Water Hardness & Quality Report (2026)

Bath, the World Heritage city in the Avon valley in Bath and North East Somerset, is supplied by Wessex Water drawing from the River Avon and its tributaries draining the Cotswold limestone country. The Avon flowing through Bath has traversed the Cotswold Jurassic limestone plateau east of the city, and its tributaries drain the Limestone hills of Wiltshire and Somerset. The Wiltshire Avon and Bristol Avon headwaters drain across Jurassic Oolitic Limestone (Great Oolite and Inferior Oolite) formations, accumulating dissolved calcium carbonate. Wessex Water supplements river abstraction with groundwater from Jurassic limestone and Triassic aquifer sources in Somerset and Wiltshire. The city's supply is treated before distribution. Bath's geological fame rests on the natural thermal springs — fed by deep limestone groundwater that has circulated through Carboniferous limestone at depth — and the domestic supply reflects the same mineral-rich Cotswold and Jurassic limestone geology.

Bath's hardness of 214 mg/L (15.0°Clark) reflects the Cotswold Jurassic Limestone influence on the Avon catchment. The Cotswold Hills are formed from Jurassic Bath Stone (Oolite) — the same warm honey-coloured limestone quarried at nearby Box and Corsham that built Bath's Georgian terraces and gave the city much of its character. This oolitic limestone is porous and reactive, dissolving readily in percolating water to yield calcium-rich groundwater and spring flows. The Avon accumulates this calcium-rich drainage throughout its Cotswold traverse. The Drinking Water Inspectorate (DWI) classifies Bath's supply as hard.

Limescale is a regular household concern in Bath. At 214 mg/L, limescale forms in kettles within two to three weeks and monthly descaling is advisable. Combi-boiler heat exchangers accumulate deposits steadily — annual servicing with a limescale check and fitting an in-line scale inhibitor are recommended. Showerheads, taps, and the marble and stone bathroom surfaces common in Bath's period properties develop regular limescale deposits. Washing-up liquid lathers moderately. The city's hard limestone water gives Bath the same water chemistry that made its natural thermal baths famous over two thousand years of occupation.