Dissolved calcium and magnesium salts, which cause water hardness, can cause a very serious loss of efficiency in boiler systems, boilers and household appliances when they are removed from the water as the water temperature rises.

These deposits could be removed chemically with acidic detergents, but they are difficult to access, so great care must be taken to prevent precipitation.

In the case of ion exchange annealing, the resin charge in the equipment replaces these hardness-causing ions in the water with sodium ions, which are not precipitated by the temperature difference.