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  • Hardness

    About 80% of the water we supply is from groundwater sources - it is generally hard after dissolving calcium and magnesium salts as it percolated through layers of limestone, chalk or rock. Signs of hard water are poor lathering of soap and limescale. The rest comes from surface water stored in reservoirs which is generally softer. 

    There is no maximum limit for the hardness of drinking water. The hardness of water is expressed in several ways including milligrams per litre of calcium carbonate (mg CaCO3/l). This is the equivalent of parts per million (ppm).  As a general indication water is classified as follows:

    • hard water – more than 200 mg CaCO3/l
    • moderately hard water – 100-200 mg CaCO3/l
    • soft water – less than 100 mg CaCO3/l.

    Find out more about limescale and how to minimise the effects on your household appliances.

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