Water hardness can be evident as white "chalky" deposits on hot and cold water fixtures, soap deposits ("soap scum"), and rings around the bathtub.  Hard water can make laundering clothing more difficult, and requires the use of more soap when bathing and cleaning. Water softeners act to remove the hardness, and levels of iron and manganese, from your water.

Water softeners contain a control valve, that directs water flow during the regeneration cycle, a resin tank that contains the cation exchange resin, and a brine (salt) tank that hold the salt used during regeneration.  Sodium and potassium is found in salt, as sodium chloride (NaCl) or potassium chloride (KCl).  Salt is commonly available at most supermarkets, home centers, or plumbing supply stores in 40 or 50 pound bags.  

The water softening process is accomplished by a chemical cation exchange that replaces the calcium and magnesium in your water with a equivalent number of sodium or potassium ions.  During the softening process, your household water passes through the resin bed, and the magnesium and calcium are removed.  A given sized resin bed has a fixed capacity to remove hardness before it needs to be regenerated to full capacity in order to continue provide softened water (for example, one cubic foot of resin has the ability to remove 32,000 grains of hardness from your water).  When the resin bed is nearing exhaustion, the control valve washes the resin bed, and draws salt containing solution from the brine tank through the resin.  As the salt contacts the resin bed, the process of ion exchange occurs, and the magnesium and calcium (hardness) that was collected in the bed during operation is washed to drain.  After a final rinse to remove the excess salt, the resin bed is again ready to provide softened water