Hard water retards the cleaning action of soaps and detergents, causing an expense in the form of extra work and cleaning agents. Furthermore, when hard water is heated it deposits a hard scale on heating coils, cooking utensils, and other equipment with a consequent waste of fuel. The scale formed by hard water coats the inside of distribution system piping, which can eventually cause significant reductions in its water carrying capacity. Soft water, on the other hand, tends to be more corrosive.

 A Hardness of 75 to 100 mg/l as CaCO3 is usually considered optimal for domestic water. Water harder than 300 mg/l as CaCO3 is generally unacceptable. Lime soda ash or ion exchange softening processes can be used to produce acceptably soft water.

 Calcium and magnesium salts, the most common cause of hardness in water supplies, are divided into two general classifications: carbonate, or temporary, hardness and noncarbonate, or permanent, hardness. Carbonate hardness is called temporary hardness because heating the water will usually remove it. When the water is heated, bicarbonates break down into insoluble carbonates that precipitate as solid particles which adhere to a heated surface and the inside of pipes. Noncarbonate hardness is called permanent hardness because it is not removed when water is heated. Noncarbonate hardness is due largely to the presence of the sulfates and chlorides of calcium and magnesium in the water.