The current definition of hardness is the sum of the calcium and magnesium concentrations, expressed as mg/l of calcium carbonate;
Total hardness = (2.497 x Calcium) + (4.118 x magnesium).
Temporary hardness is due to the presence of bicarbonates of calcium and magnesium and can be removed by boiling whereas permanent hardness is attributed to other salts such as sulphate and chlorides, which cannot be removed by boiling. Excessive hardness of water causes scaling in plumbing and heating appliances and is often a nuisance in personal hygiene. Excessive softness leads to aggressive and corrosive water properties which is a concern for copper plumbing. Hardness is classified as follows:
Hardness Range (mg CaCO3/l)
Description of Hardness
The total hardness in water is beneficial to health as it contributes to the need for the essential elements calcium and magnesium. Very hard water should be avoided by individuals with a history of kidney and gall-bladder stones and infants under the age of one year. Very hard water impairs the lathering of soap and also affects the taste of water especially for brewing tea or coffee. Very hard water can be treated using cation exchange softening.