Daventry Water Hardness & Quality Report (2026)

Daventry, the West Northamptonshire market town set on a hill above the Nene valley headwaters, is served by Anglian Water. Supply to west Northamptonshire draws on two geological sources: boreholes into the Jurassic Oolitic Limestone Aquifer — the Northampton Sand (Inferior Oolite) and Great Oolite limestone formations that underlie the Northamptonshire uplands — and blending with chalk groundwater from the Cretaceous Chalk Aquifer to the east, which enters the Northamptonshire water supply grid via transfer from Anglian Water's east Midlands network. Water is treated at Duston Water Treatment Works near Northampton before distribution west to Daventry. The very high TDS of 718.3 mg/L for a hardness of 251 mg/L reflects the long-residence character of the Jurassic limestone groundwater and possible contributions from the Lias Clay and Oxford Clay interbedded with the limestone that add sulphate and sodium ions.

The Jurassic Oolitic Limestone of the Northamptonshire plateau — the same stone quarried as Northamptonshire ironstone building material — is a productive aquifer whose relatively open pore structure allows calcium bicarbonate to dissolve from the oolite grains over long groundwater residence periods. The Great Oolite in particular is a major water-bearing horizon across the English Midlands limestone belt. At 251 mg/L Daventry's supply approaches the very-hard threshold, driven by the sustained dissolution of Jurassic carbonate rock across the plateau's aquifer system.

At 251 mg/L Daventry's water is very hard and limescale is a prominent household issue. Kettle elements fur up within a week or two and need fortnightly descaling with citric acid. Shower screens accumulate a persistent calcium film that requires weekly chemical treatment with white vinegar to maintain clarity. Washing-up liquid needs to be used generously. Combi-boilers and white goods appliances face significant scaling risk and should have inline scale inhibitors and annual servicing as standard practice. Daventry's position at the watershed of the Nene and Avon catchments gives it a distinctive market town character; its very hard tap water is a direct product of the Jurassic limestone on which the town stands.