Define Hardness - Chemical Characteristics of Water

Caused by any polyvalent cations (mainly Calcium and Magnesium). Expressed as mg/l as CaCO₃. Causes precipitates with soap (forms scum) and reduces the effectiveness of soap.  

Carbonate hardness (also known as temporary hardness) is the hardness associated with bicarbonate and carbonate ions (alkalinity) and the remaining hardness is termed non carbonate hardness (permanent hardness) and typically is associated with sulfate and chloride.  Carbonate hardness can be removed by heating water.    

Hardness is removed by lime-soda softening process or ion exchange process (discussed later). Hardness is measured by titrating with EDTA (standard is chosen so that 1 ml titrant gives 1 mg/l as CaCO₃ hardness)