Stevenage Water Hardness & Quality Report (2026)

Stevenage, the Hertfordshire new town — England's first designated new town, established in 1946 — is supplied by Affinity Water drawing from the Hertfordshire Chalk Aquifer. Stevenage sits on the broad chalk plateau of central Hertfordshire, and Affinity Water operates licensed boreholes in the chalk at sites around the town and across east Hertfordshire, sinking into the Cretaceous Upper Chalk that underlies the entire Hertfordshire upland. Supply is supplemented with Lee Valley surface water transfers within the Affinity Water network. Water is treated at Affinity Water's Hertfordshire facilities before distribution to Stevenage and the surrounding area — a town whose rapid post-war growth to over 80,000 people required sustained chalk groundwater development across the Hertfordshire aquifer zone.

Stevenage's hardness of 201 mg/L (14.1°Clark) reflects the Hertfordshire Chalk Aquifer dominance of its supply. The chalk beneath Stevenage is part of the continuous East Anglian–Chiltern Chalk Basin — a thick Cretaceous Turonian and Coniacian Chalk sequence overlaid by variable thickness of boulder clay and glacial drift. Groundwater in the chalk carries dissolved calcium from percolation through chalk matrix and fractures, producing consistently hard water across the Hertfordshire plateau. The supply hardness is representative of the Hertfordshire chalk supply zone — harder than the Chilterns chalk at High Wycombe (173 mg/L) but somewhat softer than the thicker chalk aquifer of Cambridge (310 mg/L). The Drinking Water Inspectorate (DWI) classifies this supply as hard.

Limescale is a regular household challenge in Stevenage. At 201 mg/L, limescale forms in kettles within three to four 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 bathroom surfaces develop regular limescale deposits. Washing-up liquid lathers moderately. Maintaining a monthly descaling routine and using Calgon in the washing machine is standard household limescale management for Stevenage's chalk country supply.