Precipitating water softeners increase alkalinity of the cleaning solution and this may damage skin and other materials being cleaned. Non-precipitating water softeners use complex phosphates to sequester calcium and magnesium ions. There is no precipitate to form deposits and alkalinity is not increased. If used in enough quantity, non-precipitating water softeners will help dissolve soap curd for a period of time. Mechanical water softening units can be permanently installed into the plumbing system to continuously remove calcium and magnesium.
Water softeners operate on the ion exchange process.
In this process, water passes through a media bed, usually sulfonated polystyrene beads. The beads are supersaturated with sodium. The ion exchange process takes place as hard water passes through the softening material. The hardness minerals attach themselves to the resin beads while sodium on the resin beads is released simultaneously into the water. When the resin becomes saturated with calcium and magnesium, it must be recharged.