A water softener is a special type of filter that removes the calcium and magnesium in hard water by using plastic beads and cleans itself periodically by a process called "regeneration." Water softeners have three main components: a mineral tank, brine tank and control valve. Smaller capacity models combine the mineral tank and brine tanks into one cabinet, but the two tanks are still separated within the cabinet. The mineral tank is where the water filtration takes place and the hard water is softened (calcium and magnesium are removed).The brine tank is where a solution of salt or potassium is stored. The control valve is the device that controls the flow of water into and out of the mineral and brine tanks during regeneration.