Cirencester Water Hardness & Quality Report (2026)

Thames Water supplies Cirencester, the principal town of the Cotswolds in Gloucestershire, from the upper Thames catchment and from groundwater drawn from the Jurassic Limestone aquifer of the Cotswold Hills. Surface water is abstracted from the young River Thames above Lechlade and from tributaries draining the Cotswold limestone plateau, treated at Water Eaton and Cricklade works before distribution across the upper Thames Valley and the Cotswolds. At 183 mg/L (12.8°Clark), Cirencester's water is moderately hard, reflecting the pervasive influence of Cotswold limestone on both groundwater and river chemistry throughout this part of Gloucestershire.

The Cotswold Hills are underlain by Jurassic Oolitic Limestone — the Great Oolite and Inferior Oolite formations — a thick sequence of calcium carbonate-rich rocks that form the classic Cotswold landscape of honey-stone villages and dry valleys. The River Thames itself rises near Cirencester at Thames Head, emerging as springs from the oolitic limestone, and carries limestone-derived calcium bicarbonate from the very beginning of its course. Groundwater from the Great Oolite aquifer supplements surface water with comparable hardness characteristics from the same limestone geology.

At 183 mg/L, Cirencester's water is moderately hard with manageable limescale. Descaling the kettle every four to six weeks is recommended to maintain heating efficiency and avoid chalky deposits in drinks. The combi-boiler should be fitted with a scale inhibitor and serviced annually to check for heat exchanger deposits. Washing-up liquid works well at standard quantities. Taps and shower heads accumulate moderate limescale over several weeks; a monthly wipe with white vinegar or a mild descaling product keeps fittings clean and prevents progressive hard-water staining. Limescale in Cirencester is noticeable but not as demanding as in chalk-belt areas further east.