Thames Water water hardness
Thames Water supplies water that is typically hard.
Most of the water in the South-East of England is hard in nature.
Thames Water, on their own website, source — checked 2026-08-24
Serves around fifteen million people, almost all of them in hard water. London is the single largest hard-water market in the UK and the reason limescale is a national conversation at all. Thames describes the South East supply as hard; parts of the region will sit above this band, so check your postcode.
Correction, 2026-08-24: Thames Water describes its own supply as "hard", not "very hard".
What this means for your home
You have hard water — scale protection is worth having.
The World Health Organization notes that water at 200 mg/l or above will produce scale, and that is where this band begins. At this level limescale is a recurring cost rather than an occasional nuisance, and many boiler manufacturers require scale protection to keep the warranty valid. A softener is worth costing out properly.
Where Thames Water supplies
Regions: London, South East England
Counties and areas: Greater London, Surrey, Berkshire, Oxfordshire, Wiltshire, Gloucestershire, Kent, Essex
Supply boundaries do not follow county boundaries, and several companies may supply parts of the same county. Always check your own postcode.