The hardness of water is divided into two kinds of carbonate hardness and non carbonate hardness.
(1) carbonate hardness is mainly formed by calcium and magnesium bicarbonate hardness and a small quantity of carbonate hardness. Bicarbonate hardness is decomposed into removal of sediment from the water after heating, called temporary hardness. Ca (HCO3) = 2 (heating) CaCO3 + CO2 + H2O
(2) the hardness of the non carbonate is mainly determined by the hardness of the salts such as calcium, magnesium sulfate, chloride and nitrate. This kind of hardness can not be removed by heating decomposition method, it is also known as permanent hardness, such as MgSO4, CaSO4, etc..
Carbonate hardness and non carbonate hardness and total hardness. Calcium content in water is called calcium hardness.. The content of magnesium ion in water is called magnesium hardness.. When the total hardness of the water is less than the total alkalinity, it is called negative hardness..