Water hardness

Find out what 'hard' water means and how it affects water quality.

'Hard' water is water with a lot of calcium in it – the more it contains, the harder the water is.

This doesn't affect drinking water quality.

When rain falls it contains no calcium, but as it flows over the land and filters through rocks, it dissolves minerals and becomes harder.

How hard water is depends on local geology – water hardness varies widely throughout the UK.

Most of the water we supply is hard, as it comes from underground chalk aquifers with high levels of calcium.

We don't soften water before it reaches your taps – there's no UK or European standard for the hardness of drinking water.

  • soft water contains less than 100mg of calcium carbonate per litre
  • moderately hard water contains between 100 and 200mg of calcium carbonate per litre
  • hard water contains between 200 and 300mg of calcium carbonate per litre
  • very hard water contains more than 300mg of calcium carbonate per litre.

If we supply your drinking water, follow the link below and enter your postcode to find out how hard your water is.

How hard is your drinking water?


Limescale - how to avoid it

When hard water is heated, harmless limescale forms in water systems and appliances.

Regularly clean your kettle to prevent the 'scum' floating to the surface.

Keeping the temperature of the hot water systems below 60°C will reduce the formation of limescale in boilers, on heating elements and in hot water pipes.

Alternatively, it can be avoided by installing a household water softener

Water softeners must be fitted to comply with the Water Supply (Water Fittings) Regulations 1999Find out more information about Water Regulations.

If you've had a water softener installed it is essential to have one tap supplying unsoftened water for cooking and drinking as softeners can significantly increase the level of sodium in water.

Water UK: Looking after water in your home

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