Hard water is water that has metal cations such as calcium (Ca2+),magnesium (Mg2+) and iron(Fe2+) and bicarbonates and sulphates dissolved in it. When soap dissolves in water with high hardness, it forms an insoluble grayish white precipitate which impairs the efficacy of the soap. When hard water boils, it will form calcium and magnesium salt deposits known as boiler scale. Boiler scale will reduce the conduction of heat, influence the efficiency of boilers and impede water flow in pipes. Water hardness is commonly expressed as milligrams of calcium carbonate per liter of water (mg/L of CaCO3).