Total hardness is a total of Calcium & Magnesium salts present in water. Hard water creates operational difficulties with Boilers, Cooling plants Heat exchangers or in domestic use of water. Also Hardness in process water is a critical parameter in many chemical processes. Whenever heat transfer takes place, with water as medium, hard water creates scaling on heating surfaces making heat-transfer progressively inefficient. Daily monitoring & control of water hardness at such places is important, as it can cause inefficient operation/failure of such equipment. Indian standard IS 10500 specifies following limits for drinking water Desirable limit ( max. ) : 300 ppm Permissible limit ( max. ) : 600 ppm