HELP & SAFETY

UK Water Hardness Checker and Directory

Water spots come from the mineral in your tap water, and how much there is depends on where you live. This page does three things. It sends you to your own water company for the real figure for your address, it turns that figure into the official hardness band in any unit, and it tells you what that band means when you wash a car.

Why this is not a postcode map: hardness is set by the supply zone your street is on, and two streets in the same postcode area can be on different sources. Only your water company holds the current figure for your address. We link you straight to it instead of guessing.

Step 1: get your figure from your water company

Find your supplier below. Its name is at the top of your water bill. Each link goes to that company's own hardness or water quality lookup.

Water company Main area What the company says Lookup
Affinity Water Parts of Hertfordshire, Bedfordshire and north west London, including Watford, St Albans, Luton and Stevenage, plus Folkestone and Dover No summary for the whole region. Use the lookup. Check hardness
Anglian Water East of England, including Norwich, Peterborough, Lincoln, Northampton, Milton Keynes, Ipswich and Colchester If you live in the East of England, it's likely you'll have hard water. Check hardness
Bristol Water Bristol and the surrounding area all the water in the Bristol Water area is classed as moderately hard to very hard Check hardness
Cambridge Water Cambridge and South Cambridgeshire All of the water we supply is 'hard' Check hardness
Dŵr Cymru Welsh Water Most of Wales, including Cardiff, Swansea, Newport and Bangor, plus Hereford Says its sources range from upland reservoirs to boreholes, so hardness depends on where you live. Check hardness
Essex and Suffolk Water Parts of Essex and Suffolk, including Chelmsford, Southend and Lowestoft No summary for the whole region. Use the lookup. Check hardness
Hafren Dyfrdwy Parts of mid and north east Wales, including Wrexham, Welshpool and Newtown No summary for the whole region. Use the lookup. Check hardness
Northern Ireland Water All of Northern Ireland No summary for the whole region. Use the lookup. Check hardness
Northumbrian Water North east England, including Newcastle, Sunderland, Durham and Middlesbrough No summary for the whole region. Use the lookup. Check hardness
Portsmouth Water Portsmouth, Gosport, Fareham, Havant, Chichester and Bognor Regis its chalk source means that it is moderately hard Check hardness
Scottish Water All of Scotland Says most Scottish supplies are soft to slightly hard. Check hardness
SES Water East Surrey and parts of south London, including Sutton, Reigate, Redhill, Dorking and Leatherhead we soften the water slightly as part of the water treatment process Check hardness
Severn Trent The Midlands, including Birmingham, Coventry, Leicester, Nottingham, Derby, Stoke on Trent, Gloucester and Shrewsbury Most of the water we supply ranges from soft to moderately hard Check hardness
South East Water Parts of Kent, Sussex, Surrey, Hampshire and Berkshire, including Maidstone, Tunbridge Wells, Eastbourne and Basingstoke Most of the water we supply in Southern England comes from underground chalk aquifers, so the water is hard. Check hardness
South Staffs Water Parts of Staffordshire and the West Midlands, including Walsall, Lichfield, Cannock, Sutton Coldfield and Burton upon Trent All of the water we supply is 'hard' Check hardness
South West Water Devon and Cornwall, including Plymouth, Exeter, Torquay and Truro the only area that we supply that's considered to have hard water is East Devon Check hardness
Southern Water Parts of Kent, Sussex, Hampshire and the Isle of Wight, including Southampton, Brighton, Worthing and Hastings No summary for the whole region. Use the lookup. Check hardness
Thames Water London and the Thames Valley, including Oxford, Reading, Swindon and Guildford all the water in our region is hard Check hardness
United Utilities North west England, including Manchester, Liverpool, Preston, Lancaster and Carlisle The majority of raw water in the North West comes from upland surface water reservoirs which are soft or very soft. Check hardness
Wessex Water Somerset, Wiltshire, Dorset and Bath, including Taunton, Yeovil, Salisbury and Poole Says about 80% of its water comes from groundwater, which is generally hard. Check hardness
Yorkshire Water Yorkshire, including Leeds, Sheffield, Bradford, York and Hull No summary for the whole region. Use the lookup. Check hardness
  • The towns are examples to help you find the right row. Company boundaries do not follow county lines, so trust your bill over this list.
  • Bournemouth Water is part of South West Water and Hartlepool Water is part of Anglian Water. Each has the same kind of lookup on its own website.
  • Some new housing estates are served by smaller licensed suppliers. The name on the bill is the one to ask.
  • Quotes were copied from each company's website on 5 October 2026.

Step 2: convert it and find your band

Water companies report hardness in different units. Enter the figure exactly as your company gives it.

The hardness bands in every unit

The band names and limits are the ones used by the Drinking Water Inspectorate, which regulates drinking water in England and Wales. The other units are worked out from the calcium carbonate figure.

Band mg/l calcium carbonate mg/l calcium Clark degrees German degrees French degrees
Soft Up to 100 Up to 40 Up to 7 Up to 5.6 Up to 10
Slightly hard 100 to 150 40 to 60 7 to 10.5 5.6 to 8.4 10 to 15
Moderately hard 150 to 200 60 to 80 10.5 to 14 8.4 to 11.2 15 to 20
Hard 200 to 300 80 to 120 14 to 21 11.2 to 16.8 20 to 30
Very hard More than 300 More than 120 More than 21 More than 16.8 More than 30
  • Conversion. Multiply mg/l calcium carbonate by 0.4 for mg/l calcium, by 0.07 for Clark degrees, by 0.056 for German degrees and by 0.1 for French degrees. These are the factors United Utilities publishes.
  • Dishwasher and washing machine settings usually ask for Clark, German or French degrees, which is why water companies quote them.
  • Some companies split the soft band in two. United Utilities and Severn Trent call 0 to 50 soft and 51 to 100 moderately soft. The limits above 100 are the same.
  • There is no legal limit. UK drinking water rules set no standard for hardness, so a high figure is not a fault with your supply.

What each band means when you wash a car

The middle column is arithmetic: the weight of chalky mineral in ten litres of water, which is what is left on the car if that water dries on it. The advice column is our own guidance, not a measured threshold.

Band Mineral in 10 litres What to do
Soft Up to 1 g Spots are light. Dry the car anyway, because any tap water leaves some mineral.
Slightly hard 1 to 1.5 g Wash in the shade and dry straight after the final rinse.
Moderately hard 1.5 to 2 g Work a panel at a time in warm weather. Do not leave the car to air dry.
Hard 2 to 3 g Rinse with an open flow so less water stays on the panel, then dry at once. Expect thinner foam.
Very hard More than 3 g Never let it dry on the car. A final rinse with deionised water or clean rainwater is worth the effort.
  • Do not add extra shampoo to fight hard water. Hard water does make detergents foam less, but a stronger mix costs more and takes longer to rinse. Stay at the label ratio. If snow foam looks thin, check the setup with the foam cannon orifice calculator first.
  • Drying is what prevents spots. A Twisted Loop Drying Towel takes the water off before the mineral is left behind.
  • Deionised water has had its dissolved minerals removed, so it dries without marks as long as the filter resin is still working.
  • Old spots that will not wash off may have etched the clear coat. Our guide to water spots and hard water explains the two kinds and how to deal with each.

Where the hard water is

  • Hardness follows the rock the water has passed through. Water drawn from chalk and limestone is hard. Water collected in upland reservoirs is soft.
  • That is why the companies in the south and east of England describe their water as hard, and those in the north west, the far south west and Scotland describe theirs as mostly soft. Their own words are in the table above.
  • It is never uniform. South West Water supplies mostly soft water but names East Devon as hard. United Utilities supplies mostly soft water but uses harder boreholes in the south of its region.
  • The Drinking Water Inspectorate publishes a map of typical hardness in England and Wales, with a warning that local variation is not shown and that you should ask your water company for an accurate figure.

Common questions

How do I find out how hard my water is?

Ask your water company. Each one publishes hardness for your address or supply zone on its website, usually through a postcode search. The directory on this page links to all of them.

What counts as hard water in the UK?

On the Drinking Water Inspectorate scale, water above 200 mg/l as calcium carbonate is hard and above 300 is very hard. Up to 100 is soft.

How do I convert Clark degrees to mg/l?

Divide Clark degrees by 0.07 to get mg/l as calcium carbonate. 14 Clark degrees is 200 mg/l. The converter on this page handles Clark, German and French degrees.

Does hard water damage car paint?

The water itself does not. The mineral it leaves when it dries can. Fresh spots wash off. Spots left to bake on repeatedly can etch the clear coat and then need polishing.

Should I use more shampoo in a hard water area?

No. Keep to the dilution on the label. Hard water reduces foam, but the fix for water spots is drying the car, not a stronger mix.

Is rainwater soft?

Yes. Rain has not passed through rock, so it carries very little dissolved mineral. Clean rainwater from a butt works well for rinsing.

Where the figures come from

You are welcome to link to this page. If a link in the directory has moved, tell us at hello@soapx.co.uk and we will fix it.