A hard water softener is an appliance that uses sodium chloride, also known as salt, to treat hard water. In water softening process the water supply passes through the water softener over resin beds, rows of resin beads perform an ion-exchange.A water softener is a unit that is used to soften water, by removing the minerals that cause the water to be hard. 2.3 Why is water softening applied? Water softening is an important process, because the hardness of water in households and companies is reduced during this process.