Water softening is the reduction of the concentration of calcium, magnesium, and other ions in hard water. These “hardness ions” can cause a variety of undesired effects including interfering with the action of soaps, the build up of scale, which can foul plumbing, and galvanic corrosion.^[1] Conventional water-softening appliances intended for household use depend on an ion-exchange resin in which hardness ions are exchanged, that is, trade places with, sodium ions. Water softening may be desirable where the source of water is hard.^[2] However, hard water also conveys some benefits to health by providing dietary calcium and magnesium and reducing the solubility of potentially toxic metal ions such as lead and copper.