Hard water is water that has high mineral content. Hard water is formed when water percolates through deposits of limestone and chalk which are largely made up of calcium and magnesium carbonates.
It is not always essential to remove hardness from water since it is not going to create any health related issues.The advantage of hardness actually appears in the form of decrease in quantity of soap consumption, lower maintenance cost in plumbing system and improved taste.
As a rule, permissible range of hardness in public water supply generally ranges between 75 to 115 mg/l.
Now, there are two types of hardness:
1. Temporary or Carbonate Hardness
Hardness caused by the carbonates and bi-carbonates of calcium and magnesium. This can be removed either by BOILING or ADDING LIME.
Boiling gives satisfactorily result only in case of hardness caused by calcium and not by magnesium because carbonate and bicarbonate of calcium on heating gives precipitate of calcium carbonate which can be removed easily, but on heating magnesium bicarbonate gives magnesium carbonate which is soluble in water and can’t be removed easily.
For removing magnesium hardness, we add lime, generally hydrated lime (calcium hydroxide), which gives insoluble magnesium hydroxide when treated with magnesium carbonate, which can be separated easily. Adding lime with magnesium bi-carbonate gives insoluble magnesium hydroxide and calcium bi-carbonate(which can be removed on heating; same as explained above),
2. Permanent Hardness or Non-carbonate Hardness
Hardness caused by sulphates, nitrates and chlorides of calcium and magnesium ions. These can be removed by lime soda process, base-exchange process, and demineralisation process.
Therefor at home, BOILING and LIME ADDITION can be followed as a cheap and easy way.