Thornbury Water Hardness & Quality Report (2026)

Bristol Water supplies Thornbury, the market town in South Gloucestershire north of Bristol — a pleasant historic town with a Tudor gatehouse, an independent high street, and a community that acts as a gateway to the Vale of Berkeley and the Severn Estuary's industrial waterfront heritage — from the River Avon and Mendip Hills Carboniferous Limestone spring blend in the South Gloucestershire supply zone, treated at Purton Water Treatment Works near Sharpness. At 228 mg/L (16.0°Clark) and a TDS of 652.4 mg/L, Thornbury's water is hard — with an elevated TDS/hardness ratio (2.86) reflecting calcium and sulphate contributions from the productive Carboniferous Limestone and Dolomite of the Mendip Hills aquifer system.

Thornbury lies in the South Gloucestershire lowland where Bristol Water supplies from a blend of River Avon surface water and Mendip Carboniferous Limestone groundwater and reservoir contributions. The Mendip limestone aquifer dissolves calcium carbonates and limited sulphate from gypsum veins to produce 228 mg/L with TDS 652.4 mg/L at Thornbury — hard water consistent with the broader Bristol and South Gloucestershire hard water supply tier, similar to adjacent communities in the same Bristol Water south Gloucestershire distribution zone.

At 228 mg/L, limescale is a persistent household challenge in Thornbury. Kettles should be descaled monthly. The combi-boiler benefits from a fitted scale inhibitor and annual professional servicing. Washing-up liquid requires more product per wash. Taps and shower heads develop visible white limescale deposits within one to two weeks; a fortnightly wipe with white vinegar or a proprietary descaling product keeps fittings clean. The hard Mendip limestone-influenced supply at Thornbury is characteristic of the Bristol Water South Gloucestershire distribution network — the Carboniferous Limestone aquifer delivering hard, mineralised water to communities across the Bristol urban fringe.