How hard is my water?

Part of our hard water guide

Your kettle has a crust and the shower screen never looks clean. Is that just life in a hard water area, or something you can sort out?

By Andrew Tomlinson, WaterKit · Last reviewed 24 October 2026

What is hard water?

Hard water is water with a lot of dissolved calcium and magnesium in it. Rain is naturally soft. It picks up those minerals as it soaks through rock, and limestone and chalk give up the most. So the hardness of your tap water is really a geology lesson about where it came from.

There are two kinds. Temporary hardness (the carbonate part) is what turns into limescale when you boil water. Permanent hardness doesn't form scale when heated. The scale in your kettle comes from the temporary kind.

How is water hardness measured?

In the UK, hardness is usually given in milligrams of calcium carbonate per litre (mg/l, sometimes written mg/l CaCO₃ or ppm, which means the same here). Some water companies, appliance manuals and older reports use degrees instead. To convert:

So 300 mg/l is about 21 °Clark or 17 °dH. One trap to avoid: some websites say 1 degree equals 17.1 ppm. That's an American unit (grains per gallon), not a Clark degree.

Is my water hard or soft?

The Drinking Water Inspectorate (DWI) groups UK water like this:

There's no single official scale, so you'll see slightly different bands elsewhere. South West Water, for example, splits soft into soft (up to 50) and moderately soft (51 to 100). The numbers matter more than the labels.

Do I live in a hard water area?

Roughly, the further south and east you go in England, the harder the water gets. The British Geological Survey says groundwater makes up over three quarters of the public supply in south-east England, and the region relies heavily on the chalk. Water that soaks through chalk comes out hard.

• Hard to very hard: Anglian Water says all of the water in its region is hard to very hard, and Southern Water says most of its water is hard because it comes from underground chalk.
• Soft to very soft: United Utilities says most water in the North West is soft or very soft, because it comes from upland reservoirs. South West Water says most of its water comes from moorland rivers and reservoirs and is soft or moderately soft. Scotland's regulator says most Scottish water is soft, because chalk and limestone aren't common there.

For real numbers, our guide to which UK town has the hardest tap water lists the hardest zones we found, and the water hardness by town pages cover individual towns. Manchester readers: here's whether Manchester water is hard or soft.

How do I find out my exact hardness?

Two ways, and they answer slightly different questions.

Your water company's postcode lookup tells you the typical hardness of the supply zone you're in. Severn Trent, Southern Water and United Utilities all have one, and so does Thames Water on its website. Our guide on how to check your water hardness by postcode walks you through it.

Testing your own tap tells you what's actually coming out in your kitchen. That's the number that matters if you have a softener, a filter, a borehole or a supply zone that blends water from different sources.

Is hard water bad for you?

No. UK regulations set no standard for hardness, calcium or magnesium, and the World Health Organization says hardness isn't of health concern at the levels found in drinking water. Southern Water and Scotland's regulator both describe hard water as safe to drink.

The WHO also notes that drinking water can contribute some of the calcium and magnesium in your diet. Some studies have linked harder water with heart health, but the WHO says that evidence is debated and doesn't prove cause and effect. In short: hard water affects your kettle far more than it affects you.

Does hard water cause hair loss or dry skin?

Hair. The evidence is thin and mixed. A small 2013 lab study found hard water made no difference to hair strength or elasticity. A 2018 lab study, which soaked hair samples for three months, found hair treated with hard water was a little weaker. Neither looked at hair loss in real people. There's no good evidence hard water makes hair fall out.

Skin. The NHS lists hard, chalky water among the things that can irritate skin in contact dermatitis, and Great Ormond Street Hospital says hard water is one of the things that can dry the skin and make eczema worse. A 2016 UK study of 1,303 babies, led from St George's, University of London and King's College London, found eczema was more common in hard water areas, though it showed a link rather than a cause. A 2011 trial found that fitting a water softener gave children with eczema no extra benefit over usual care. If you're worried about eczema, talk to your GP or pharmacist.

What does hard water do to my home?

It builds up limescale. The DWI describes limescale as deposits of calcium and magnesium that build up on heating elements over time, shortening their life and making them less efficient. The WHO makes the same point about anything that heats water.

Building guidance in Scotland goes further. It says the water feeding water heaters and the hot water side of combi boilers should be treated where hardness is over 200 mg/l. Day to day, hard water means more descaling, chalky marks on glasses and taps, and more detergent and soap to get a lather.

Can I soften hard water?

Yes. A plumbed-in softener swaps calcium and magnesium for sodium and removes most of the hardness, while a filter jug only takes some of it out. If you soften, the DWI advises keeping an unsoftened kitchen tap for drinking and cooking. Our guide Do I need a water filter or a water softener? compares the options and costs.

How do I test my water hardness?

Dip a strip. One WaterKit strip gives your hardness in 60 seconds, along with 19 other readings. The hardness pad reads in steps of 0, 25, 50, 100, 250 and 425 mg/l. Between 100 and 250 the colour sits between two steps, so you'll get a range rather than an exact figure. The alkalinity and carbonate pads next to it give a rough idea of how much of it is the scale-forming kind, and the results checker tells you which band you're in and what to do about it.

It's most useful when you compare:

• Your tap against your water company's figure. They should be close. If not, something in your home is changing the water.
• Before and after a softener. Softened taps should drop sharply, while your unsoftened kitchen tap stays where it was.
• Your filter jug against the tap. See how much it really takes out.

Best pack: 50 strips, enough to test now and again after any change, £8.99 (or £13.99 with a bacteria test), with free 2nd Class delivery on every order. See the kit

Your hard water questions

How can I tell if my water is hard or soft?

Look up your postcode on your water company's website and compare the figure with the DWI bands: soft is up to 100 mg/l and hard is over 200 mg/l. Kettle scale and poor lather are the everyday signs. A test strip gives you the figure for your own tap.

Is London water hard or soft?

Hard. Thames Water says most of the water in the South East of England is hard. Use its postcode lookup for your exact figure.

Is hard water safe to drink?

Yes. There's no UK health standard for hardness, and the WHO says it isn't of health concern at the levels found in drinking water.

How do I convert Clark degrees to mg/l?

Multiply by about 14.3. So 15 °Clark is roughly 214 mg/l, which is hard.

Does hard water cause hair loss?

There's no good evidence that it does. Small lab studies on hair strength disagree, and none has measured hair loss in people.

At what hardness is a softener worth it?

Most people start to notice real limescale problems above about 200 mg/l, which the DWI calls hard. Below 100 mg/l, there's little to soften.

Sources

1. Drinking Water Inspectorate, Water hardness (bands; no UK standard; limescale; unsoftened drinking tap).
2. World Health Organization, Hardness chemical fact sheet and background document.
3. The Water Supply (Water Quality) Regulations 2016, Schedule 1 (no hardness parameter).
4. United Utilities, Water hardness factsheet (conversion factors; temporary and permanent hardness; North West soft water).
5. Southern Water, Hard water checker.
6. Severn Trent, Check my water quality.
7. Thames Water, thameswater.co.uk (hard water page and postcode lookup). Anglian Water's and South West Water's hard water factsheets are cited by name.
8. Drinking Water Quality Regulator for Scotland, Water hardness FAQ.
9. British Geological Survey, Groundwater resources in the UK.
10. Srinivasan G. et al., Effects of hard water on hair, International Journal of Trichology, 2013; Luqman M.W. et al., Effect of topical application of hard water in weakening of hair, International Journal of Trichology, 2018.
11. Perkin M.R. et al., Association between domestic water hardness and eczema in infancy, Journal of Allergy and Clinical Immunology, 2016; Thomas K.S. et al., Softened Water Eczema Trial, PLoS Medicine, 2011.
12. NHS, Contact dermatitis: causes; Great Ormond Street Hospital, Eczema.
13. Scottish Government, Domestic Building Services Compliance Guide 2022 (treat boiler feed water above 200 ppm).
14. WaterKit Water Test Kit and results checker (hardness pad steps 0 to 425 mg/l).

Contains public sector information licensed under the Open Government Licence v3.0.