When heated, calcium carbonate and magnesium carbonate are removed from the water and produce a scale buildup in the hot water heater. A large scale buildup slows the heating process and requires more energy to heat water. Water heaters with large accumulations of mineral buildup will have shorter life spans. Scale deposits also corrode and plug plumbing fixtures and accumulate in other appliances affecting their performance. Water softeners are cation exchange devices.
Cations refer to positively charged ions.
Cation exchange involves the replacement of the hardness ions with a nonhardness ion. Sodium ions are supplied from dissolved sodium chloride salt, also called brine. In the ion exchange process, sodium ions are used to coat an exchange medium in the softener. Sodium ions are held loosely and are easily replaced by calcium and magnesium ions. During this process free sodium ions are released to the water.