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How do I know if my water is hard or soft?

Water hardness is caused by dissolved calcium and magnesium. The hardness of water supply in the UK will very depending on location. The hardness of water, expressed in mg/L CaCO3 (calcium carbonate), can be classified as shown below:

  Water Hardness (mg/L CaCO3)
Soft up to 100
Slightly hard 100 -150
Moderately hard 150 – 200
Hard 200 – 300
Very hard More than 300


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