Sudbury Water Hardness & Quality Report (2026)

Sudbury, the south-west Suffolk market town on the River Stour made famous by Thomas Gainsborough — the Stour valley landscape painter — is supplied by Essex & Suffolk Water from the River Stour and the Suffolk Chalk Aquifer. The River Stour is a classic chalk stream rising on the chalk uplands of south-west Suffolk and north-west Essex near Haverhill, flowing east through Sudbury to the Dedham Vale (Constable country) and the estuary at Manningtree. Essex & Suffolk Water abstracts from the Stour at Sudbury and from chalk boreholes in the south Suffolk chalk dip slope, treating the supply at Langham Water Treatment Works on the Stour near Colchester. The chalk character of both the Stour river water and the chalk borehole component produces consistent hard water at 205 mg/L in the Sudbury supply zone — modestly softer than Haverhill (218 mg/L) upstream, reflecting greater Stour surface-water dilution and a shorter chalk residence path for the Stour at Sudbury than the pure borehole supply at Haverhill.

The River Stour at Sudbury carries chalk-discharged spring water from the south Suffolk and north Essex chalk, maintaining calcium bicarbonate levels of 200–220 mg/L even in periods of higher flow. The chalk borehole component in the Sudbury supply adds concentrated chalk groundwater of 210–230 mg/L. The combination produces the characteristic 205 mg/L hardness of the Stour valley supply at Sudbury — hard but somewhat diluted by river flow compared with pure borehole-dominated supplies in the east Suffolk coastal zone. The TDS of 458.3 mg/L is consistent with chalk carbonate chemistry.

At 205 mg/L Sudbury's water is hard and limescale is a regular feature of domestic maintenance in Gainsborough's town. Kettles benefit from monthly descaling with a commercial descaler. Shower screens and bath taps develop calcium deposits requiring regular white vinegar treatment. Washing-up liquid must be used generously. Combi-boilers benefit from inline scale inhibitor protection. Sudbury's beautiful Stour valley setting — the meadows and mill ponds that Gainsborough painted — conceals the hard chalk water that has characterised the Stour since it first began draining the chalk downs above Haverhill.