In places where water is hard, people install watersoftener upstream of water heater to prevent scale (Calcium & Magnesium ions) build up in the heating coil. Normally, a water softener consists of rasin polymer, which exchanges Calcium & Megnesium ions with Sodium ion. After a while, the rasin will be full of Calcium & Magnesium and need to be regenerated by rinsing in strong brine solution (salt water). In short, salt rocks is used to soften the water. But rasin is rinsed with fresh water after regeneration so soften water does not have salty taste, just the sodium ion.