Softening is the process of removing calcium and magnesium ions from water by cation exchange. It is typically used to reduce the crusting tendency of water used in boiler water supply, or to increase the foaming effect of detergents, especially in washing and processes. Calcium and magnesium ions in the solution are exchanged for sodium ions bound to the cationic resin. When water passes through this resin, calcium and magnesium ions in the water are replaced by sodium ions and adsorbed on the resin. The regeneration process "cleans" the resin with a high concentration salt solution (15-30% NaCl). As a result, Ca or Mg adsorbed on the resin is replaced with Na.

• Used particularly in laundries & process, calcium and magnesium ions in solution are exchanged for sodium ions attached to a cationic resin