Water hardness by postcode: is my water hard or soft?

Enter your postcode to check the supplier’s reported hardness, its reporting period and the units you need for your appliances.

Supplier-verified postcode matching currently covers Thames Water, Affinity Water, Yorkshire Water, Severn Trent Water and United Utilities, plus Northern Ireland Water’s published annual postcode mapping. See which suppliers are covered · Find Scottish hardness and zone history

How the postcode check works

Your water supplier, not your council or postcode district, decides which treatment works and supply area serve your home. When you enter a full postcode, WaterGrade asks the supplier’s own lookup which supply area it belongs to. We then show the approved report we hold for that area: the published hardness in mg/l as calcium carbonate, the reporting period, sample information where the supplier gives it, and a link to the original document.

If a supplier returns more than one area, or no area at all, we say so and send you to the supplier’s address-level checker. We never substitute a nearby town’s result, and a missing result does not mean your water is soft.

Which suppliers the checker covers

Postcode matching works for these suppliers. Coverage inside each supplier depends on the approved reports we hold, and reporting periods differ between suppliers.

Thames Water — London and the Thames Valley, matched through the supplier’s own postcode lookup
Affinity Water — Parts of London, South East and eastern England, matched through the supplier’s own postcode lookup
Yorkshire Water — Yorkshire, matched through the supplier’s own postcode lookup
Severn Trent Water — The Midlands and adjoining areas, matched through the supplier’s own postcode lookup
United Utilities — North West England, matched through the supplier’s own postcode lookup
Northern Ireland Water — Northern Ireland, matched through the supplier’s published annual postcode mapping

Other suppliers: use the official checker

We do not yet match postcodes for these suppliers. Their own websites publish local water-quality and hardness information:

Not sure who supplies you? Find your water company.

Worked example: reading a result

Affinity Water’s approved report for the Woking supply area, associated with Woking, gives total hardness of 273 mg/l as calcium carbonate (reporting period: 2025). On the scale below that is hard.

Appliance manuals often use other units. The same published value is about 19.1 Clark degrees, 15.3 German degrees (°dH) or 2.73 mmol/l. These are conversions of one reported area value, not another test.

See the full Woking report — the supply at your address may differ, so check your own postcode.

Read the hardness scale

These categories use mg/l as calcium carbonate. They describe mineral hardness, not a health score.

Hardness	mg/l as CaCO₃
Soft	Up to 100
Slightly hard	Above 100 to 150
Moderately hard	Above 150 to 200
Hard	Above 200 to 300
Very hard	Above 300

Source: Drinking Water Inspectorate hardness guidance.

What should I do with the result?

Use the conversion on your result page to match the unit in your appliance manual. Follow the manufacturer’s instructions for settings and maintenance. If you want to test the water at your tap, choose a test that answers your specific question.

Test hardness at home Convert hardness units Set your dishwasher Hard vs soft water Descale a kettle Remove limescale

Frequently asked questions

How do I find my water hardness by postcode?

Enter your full postcode in the checker on this page. For Thames Water, Affinity Water, Yorkshire Water, Severn Trent Water and United Utilities, we ask the supplier’s own lookup which supply area serves that postcode and show its approved report, including the reporting period. For Northern Ireland Water we use the supplier’s published annual postcode mapping. For other suppliers, use the official checker links on this page.

What counts as hard water in the UK?

The Drinking Water Inspectorate describes water up to 100 mg/l as calcium carbonate as soft, above 100 to 150 as slightly hard, above 150 to 200 as moderately hard, above 200 to 300 as hard and above 300 as very hard.

Why might my result differ from a neighbour’s or from a town page?

Supply areas do not follow town or postcode-district boundaries, so nearby streets can be served from different sources. A report describes a named supply area over a stated period; it is not a test of the water at your tap today.

Does hard water mean poor water quality?

Hardness on its own does not tell you that. It describes dissolved calcium and magnesium and mainly affects limescale, soap and appliance settings. It does not show whether other drinking-water standards were met, which is why each report lists quality results separately.