Greenwich Water Hardness & Quality Report (2026)

Greenwich, the historic south-east London borough home to the Prime Meridian and the Royal Naval College, is supplied by Thames Water from a blend of Thames surface water and deep chalk groundwater. The River Thames is abstracted at Teddington and Hampton Water Treatment Works in west London and the Lee Valley Reservoir Complex further east, while chalk boreholes in the Lee Valley and north Kent chalk contribute hard groundwater to the south-east London distribution zone. Water is treated at Coppermills Water Treatment Works in Walthamstow and Kempton Park before reaching Greenwich's mains network. The very high TDS of 657.1 mg/L reflects the substantial chalk groundwater fraction in the blend, which carries concentrated dissolved calcium bicarbonate and sulphate ions.

Greenwich sits on the south bank of the Thames where the river has carved through the chalk and overlying London Clay and Thanet Sands. The underlying chalk aquifer feeds springs and contributes dissolved calcium bicarbonate to the river itself. Thames Water's blended supply for south-east London incorporates a high proportion of chalk groundwater from the East London Chalk Zone, where boreholes abstract water that has resided in the chalk for many years. This produces hardness of 256.5 mg/L — very hard by any standard, comparable to the hardest chalk-belt towns in southern England.

At 256.5 mg/L Greenwich's tap water is very hard and limescale is a constant household challenge. Kettle elements fur up within a fortnight and require monthly descaling with citric acid. Shower screens need weekly wiping and a periodic limescale treatment to maintain clarity. Washing-up liquid lathers adequately only with generous amounts. Combi-boilers — widespread in Greenwich's Victorian and Edwardian terraces — need scale inhibitors and annual servicing to remain efficient. A water softener significantly reduces daily limescale maintenance and is a worthwhile investment for any Greenwich household with old-style plumbing or hard-working white goods.