Why is water hardness measured in terms of CACO3?
The hardness of water is expressed in terms of ppm because the molecular weight of calcium carbonate is 100gm/mol. It is easy to calculate. This is one of the main reason for expressing the hardness of water in ppm. Also calcium carbonate is insoluble in water therefore it is easy to calculate its amount in water.The hardness is not entirely due to calcium – magnesium is usually present to some extent and other multivalent cations. When the hardness is expressed as CaCO3, it is calculated as if the magnesium, etc. were there as calcium. It also includes the bicarbonate ions such as chloride, sulphate and nitrate.