Portsmouth Water water hardness
Portsmouth Water supplies water that is typically moderately hard.
Our water is mainly derived from the chalk of the South Downs - it is excellent quality, but its chalk source means that it is moderately hard.
Portsmouth Water, on their own website, source — checked 2026-08-24
South Downs chalk springs. Hard throughout.
Correction, 2026-08-24: We previously showed 'hard'. Portsmouth Water describes its own supply as 'moderately hard'. Reduced to match.
What this means for your home
Your water is moderately hard — worth protecting the boiler, not much more.
Scale will build up slowly on heated surfaces. A scale inhibitor on the boiler is proportionate and inexpensive, and some manufacturers start asking for one around this level. A softener is still difficult to justify on cost. Test your own tap before deciding — at this level the exact figure matters.
Where Portsmouth Water supplies
Regions: South East England
Counties and areas: Hampshire, West Sussex
Supply boundaries do not follow county boundaries, and several companies may supply parts of the same county. Always check your own postcode.