What is hard water and why does it matter?

Hard water has a high mineral content, usually containing bigger amounts of calcium and magnesium. These minerals can build-up in your dishwasher over time, and can stop your kit from working properly. You'll know if the water's hard by the way that soap lathers. The minerals in hard water react with the soap, creating a 'scum' which floats on the surface of the water, but doesn't foam.

Using dishwasher salt can help stop these deposits, by 'softening' your water. The amount of dishwasher salt you'll need to add depends on how hard the water in your area is.

Finding out local water hardness


To use the right amount of salt, you'll need to know how hard the water is in your area. The harder the water, the more salt you'll need to use.

The best way to find out your water hardness is to check with your water supplier. We've listed providers who use hard water below, and a link to their website, so you can check the hard water levels for your area. You should re-check with them every so often (the levels can change sometimes).

Once you know the hard water level, you just need to change how much dishwasher salt you use. The user manual for your kit will show you how to adjust the salt setting for your washes. Don’t worry if you’re not sure where it is, you can find the user guide for your kit on our site here.

  • For Affinity Water (formerly Veolia Water) click here.
  • For Anglian Water, click here.
  • For Sembcorp Bournemouth Water, click here.
  • For Bristol Water, click here.
  • For Cambridge Water, click here.
  • For Cholderton and District Water, click here.
  • For Dee Valley Water, click here.
  • For Dwr Cymru - Welsh Water, click here.
  • For Essex and Suffolk Water, click here.
  • For Northumbrian Water, click here.
  • For Portsmouth Water, click here.
  • For the Drinking Water Quality Regulator for Scotland, click here.
  • For Severn Trent Water, click here.
  • For South East Water, click here.
  • For South Staffs Water, click here.
  • For South West Water, click here.
  • For Southern Water, click here.
  • For Sutton and East Surrey Water, click here.
  • For Thames Water, click here.
  • For United Utilities Water, click here.
  • For Wessex Water, click here.
  • For Yorkshire Water, click here.

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