How do I find out how hard my water is?

Hard water decides a surprising amount: how often your kettle needs descaling, how long a combi boiler's heat exchanger lasts, whether a shower head clogs, how much detergent you need, whether a water softener would pay for itself, and how quickly an immersion element fails. Most people have a vague sense of whether their area is hard, and a precise figure is more useful and takes five minutes to obtain.

Step by step

1. Look it up with your water company first.Every water company publishes hardness by postcode or supply zone on its website, and this is the authoritative figure — it comes from their routine sampling. It also tells you the units they use, which matters for interpreting anything else.
2. Understand the units.Hardness is most commonly quoted as milligrams per litre of calcium carbonate, which is numerically the same as parts per million. Degrees Clark and degrees French are older scales with completely different numbers for the same water. Always check which unit a figure is in before comparing it to anything.
3. Know the rough bands.Water companies classify supplies from soft through moderately soft, slightly hard, moderately hard, hard and very hard. Your company's own banding for your zone is the practical answer — the boundaries differ slightly between organisations and between the industry and appliance manufacturers.
4. Use a test strip for a reading at your tap.Inexpensive strips dipped in a glass of cold water from the kitchen tap give a colour reading against a chart. Useful for confirming the published figure, for checking a private supply, or for checking the output of a softener.
5. Read the evidence around the house.Scale in the kettle within weeks, white crust on the shower head and tap spouts, a scummy tidemark in the bath, soap that will not lather, cloudy glasses from the dishwasher and white spots on a shower screen all point to hard water. Their absence points to soft.
6. Check whether you are in a mixed zone.Some areas are supplied from more than one source and hardness varies through the year or between streets. If your published figure and your kettle disagree, that is often why. A test strip settles it.
7. Note it where it will be used.Write the figure and the unit inside a kitchen cupboard door. Dishwasher water hardness settings, softener salt settings, boiler descaling decisions and appliance warranties all ask for it, and looking it up each time is a nuisance.
8. Act on it.Hard water means descaling the kettle and shower head routinely, setting the dishwasher's water hardness correctly, considering scale protection on a combi boiler, and deciding whether a softener or a scale reducer is worth it. Soft water means almost none of that applies and you can stop worrying about it.

Tips

• The dishwasher has a water hardness setting that most people never touch. Setting it correctly noticeably improves results in a hard area and stops wasting salt in a soft one.
• A private borehole or spring supply is not covered by any published figure and should be tested properly — for hardness and for everything else.
• If you move house even a short distance, the hardness can change completely. Look it up again rather than assuming.
• Appliance manuals often specify descaling frequency by hardness band. That is where the figure earns its keep.

Questions people ask