Water softening is a key step in treating hard or raw water. Without this step, minerals and materials in raw water such as calcium, magnesium and various others can build up to damage the water treatment equipment; specifically the membranes used to clean water. Removal of these materials can be achieved by ion exchange.

This process involves calcium and magnesium ions being switched for sodium or potassium ions. Inside the softener, an ion exchange material, such as a bed of small, plastic resin beads or zeolite, is saturated with sodium or potassium chloride. The material draws in calcium and magnesium, which displace the sodium or potassium into the water. When the material is completely covered through exchange, a solution washes away the removed minerals and replaces the regenerate ions before the tank is rinsed with fresh water. This process is known as regeneration