What is water hardness and what causes it?

Water hardness is caused by dissolved calcium and magnesium salts in water. Temporary hardness is due to bicarbonates and can be removed by boiling. Permanent hardness is due to sulfates and chlorides and requires chemical treatment. Hard water causes scaling in pipes and boilers, reduces soap effectiveness, and affects industrial processes. Hardness is expressed in mg/L as CaCO3, with soft water having less than 75 mg/L.