Softening processes are used to reduce water hardness. Using chemicals, water hardness undergoes chemical reactions and precipitates. As a result, water hardness is reduced. Water hardness is due to the presence of carbonates, sulfates, chlorides, and nitrates of the metals calcium, magnesium, iron, and aluminum.

Hard water is a term used to describe water containing cations of calcium, magnesium, strontium, iron, manganese, etc. Since the amount of strontium, iron, and manganese in water is very low, calcium and magnesium cations are considered the main cause of water hardness.