Letchworth Garden City Water Hardness & Quality Report (2026)

Letchworth Garden City, the world's first Garden City (founded 1903) in north Hertfordshire on the chalk plateau north of the Hitchin gap, is supplied by Affinity Water from the North Hertfordshire Chalk Aquifer — the Cretaceous Chalk beneath the north Hertfordshire chalk escarpment. Affinity Water draws from deep chalk boreholes in the chalk of the north Hertfordshire plateau in the Letchworth and Baldock area, where the Upper Chalk reaches considerable thickness and groundwater has extended contact with the chalk, accumulating very high dissolved calcium. Letchworth's supply zone (249 mg/L) is significantly harder than Hitchin (173 mg/L) just four miles to the south, reflecting a different deep borehole supply zone with longer chalk groundwater residence times and higher calcium loading. The TDS of 657.9 mg/L confirms very high mineral content.

Letchworth Garden City's very hard water — 249 mg/L (17.5°Clark) — reflects the deep Cretaceous Chalk borehole supply in Affinity Water's north Hertfordshire supply zone, considerably harder than nearby Hitchin (173 mg/L) due to the different chalk borehole depth and residence time. The Drinking Water Inspectorate (DWI) classifies this supply as very hard.

Limescale is a very serious household challenge in Letchworth. At 249 mg/L, limescale forms in kettles within one to two weeks requiring fortnightly descaling. Combi-boiler heat exchangers face serious limescale risk — annual boiler servicing and a polyphosphate scale inhibitor are essential. Showerheads, taps, and shower screens develop very heavy deposits. Washing-up liquid lathers very poorly. Letchworth homeowners should strongly consider a whole-house water softener for effective protection against the very hard north Hertfordshire chalk supply.