Rickmansworth Water Hardness & Quality Report (2026)

Rickmansworth, the south-west Hertfordshire town at the confluence of the Colne, Chess and Gade — the Three Rivers district at the Chiltern edge — is supplied by Affinity Water from chalk boreholes in the Chess and Colne valley Chalk Aquifer. The River Chess is one of England's finest chalk streams, rising in the chalk hills of the Chilterns at Chesham and flowing south through Chorleywood and Rickmansworth, discharging chalk groundwater along its entire length. Affinity Water (Central region) operates borehole abstraction along the Chess valley and in the Colne gravels, augmented by groundwater from the Hertfordshire Chalk Aquifer dip slope. Water is treated at Maple Lodge Water Treatment Works near Rickmansworth before distribution through the Three Rivers supply zone. At 192.5 mg/L the hardness reflects the chalk spring-fed character of the Chess and Colne valley supply, moderated by treatment blending to produce a consistently moderately hard supply.

The Cretaceous Chalk of the Chiltern Hills dips south-east from the Chiltern escarpment, forming the unconfined chalk aquifer beneath the Chess and Colne valleys that sustains the chalk stream network. Groundwater discharging from the chalk into the Chess and Colne at 30–50 m depth carries calcium bicarbonate at 180–200 mg/L — characteristic of unconfined Chiltern chalk at these depths, harder than Thames surface water but softer than the deeply confined chalk of outer London and Berkshire. The TDS of 444.5 mg/L reflects chalk carbonate chemistry with modest additional mineral content from the Chiltern chalk horizons.

At 192.5 mg/L Rickmansworth's water is moderately hard and limescale management is a regular household routine. Kettles benefit from monthly descaling with a commercial descaler or citric acid soak. Shower screens develop a calcium haze requiring regular treatment with white vinegar. Washing-up liquid lathers adequately. Combi-boilers and white goods benefit from inline scale inhibitor protection. Rickmansworth's setting in the Chess valley — renowned for its chalk river fishing and water meadows — means the same chalk aquifer that sustains the Chess's crystal-clear ecology also determines the hardness of every kettle and shower screen in the town.