Putney Water Hardness & Quality Report (2026)

Putney, in the London Borough of Wandsworth in south-west inner London on the River Thames, is supplied by Thames Water from the River Thames reservoir complex in west London. Thames Water abstracts from the Thames at Hampton and Walton-on-Thames intake points, storing water in the west London reservoir group — Queen Mother, Wraysbury, Staines, and Walton reservoirs — before treatment at Walton Water Treatment Works. From there the treated water is pumped into the inner London distribution network for south-west London, including Putney. The Thames carries dissolved calcium from a vast chalk and limestone catchment — chalk-stream tributaries (Kennet, Wey, Mole) and the Cotswold Limestone upper Thames drainage — that accumulates through the river's southern England course, producing consistently hard water at the west London intakes.

Putney's hardness of 230.5 mg/L (16.2°Clark) is characteristic of the south-west inner London Thames supply zone — hard, but marginally softer than east London areas supplied more heavily from the chalk-dominated Lee Valley supply corridor. The reservoir storage at Hampton and Walton dilutes the peak chalk calcium slightly before treatment and distribution. The Chalk Aquifer drainage — via the Wey and Mole in Surrey — contributes the dominant calcium load to the Thames at west London intakes. The Drinking Water Inspectorate (DWI) classifies this supply as hard.

Limescale is a persistent household challenge in Putney. At 230.5 mg/L, limescale forms in kettles within two to three weeks and monthly descaling is advisable. Combi-boiler heat exchangers accumulate deposits regularly — annual boiler servicing and fitting an in-line scale inhibitor are recommended. Showerheads, taps, and shower screens develop consistent deposits. Washing-up liquid lathers poorly. The south-west London rental and property market means limescale management is a routine maintenance concern — Calgon monthly in the washing machine and a kettle descale every two to three weeks is standard Putney household practice.