Softening is a water treatment process that allows for the replacement of scaling salts (with low solubility) with more soluble salts. Water hardness can be reduced by passing it through a softener (manual or automatic) over an ion-exchange resin, which consists of a polymer carrying sodium ions (Na+) that are exchanged for the calcium and magnesium ions in the water. The calcium and magnesium ions are thus retained by the resin, which is subsequently regenerated by treatment with concentrated salt water (NaCl), also known as brine.