Check water hardness by postcode
Your hardness figure in all seven units, the °dH setting your appliances ask for, and how often a softener would regenerate for your household.
How UK hardness scales work
Two classification scales are in common use in the UK, and they disagree with each other below 100 mg/l CaCO₃.
| mg/l CaCO₃ | DWI five-band | Industry six-band |
|---|---|---|
| 0–50 | Soft | Soft |
| 50–100 | Soft | Moderately soft |
| 100–150 | Slightly hard | Slightly hard |
| 150–200 | Moderately hard | Moderately hard |
| 200–300 | Hard | Hard |
| 300+ | Very hard | Very hard |
Common questions
- What is water hardness measured in?
- In the UK the standard unit is milligrams per litre of calcium carbonate (mg/l CaCO₃), which is the same number as parts per million. Appliance manuals usually ask for German degrees (°dH), older British sources use Clark degrees, and softener manufacturers often use grains per gallon. They all describe the same measurement.
- What counts as hard water?
- The water industry's six-band scale calls anything above 200 mg/l CaCO₃ hard, and above 300 mg/l very hard. The Drinking Water Inspectorate uses a five-band scale that treats everything below 100 mg/l as soft. The two scales only differ below 100 mg/l — above that they agree.
- What should I set my dishwasher to?
- Dishwashers, washing machines and coffee machines are almost always set in German degrees (°dH). Divide the mg/l CaCO₃ figure by 17.85 to get °dH — or read it straight off the result above.
- Is hard water bad for you?
- No. Hard water is not a health risk; the calcium and magnesium that make water hard are dietary minerals. Hardness is a practical problem rather than a safety one — limescale in kettles, boilers and washing machines, and more soap or detergent needed.
- How often will a water softener regenerate?
- It depends on your hardness, how much water the household uses and the softener's resin capacity. A typical 20,000-grain cabinet unit in a hard-water area serving four people regenerates roughly weekly. The calculator above works it out for your postcode and household size.
Looking for the full picture? Check nitrate, lead, fluoride and chlorine levels for your postcode.