Water Softener

Water softening methods mainly rely on the removal of Ca²⁺ and Mg²⁺ from a solution or

the sequestration of these ions, i.e. binding them to a molecule that removes their ability to form scale or interfere with soaps. Removal is achieved by ion exchange and by precipitation methods. Sequestration entails the addition of chemical compounds called sequestration (or chelating) agents.

Since Ca²⁺ and Mg²⁺ exist as nonvolatile salts, they can be removed by distilling the water, but distillation is too expensive in most cases (rainwater is soft because it is, in effect, distilled)

Regeneration

The resin's capacity is gradually exhausted and eventually it contains only divalent ions (e.g., Mg²⁺ and Ca²⁺ for cation exchange resins, and SO₄^2- for anion exchange resins). At this stage, the resin must be regenerated. If a cationic resin is used (to remove calcium and magnesium ions) then regeneration is usually effected by passing a concentrated brine, usually of sodium chloride or potassium chloride, or hydrochloric acid solution through them. For anionic resins, regeneration typically uses a solution of sodium hydroxide (lye) or potassium hydroxide. The salts used for regeneration are released into the soil or sewer.
In industrial scale water softening plants, the effluent flow from re-generation process can precipitate scale that can interfere with sewerage systems.