This is the process of removing ions from the water and replacing them with sodium ions and chloride ions. The most common use for this is residential, where a homeowner is trying to reduce the hardness or improve the taste of the water that the municipal service provides. This also reduces deposits and scale that can be left from water with a high level of hardness. The second application is deionization. This is used in applications where extremely pure water is required.
Water flows over the resin.
The ions in the water are attracted to the resin. The ions in the water attach themselves to the resin, and knock off the ions that are already attached. The resin is exhausted when all of the replacement ions are gone. In order to replenish the resin, also called regenerating the resin, a strong solution of the replenishment ions must be applied to the resin. This removes the ions that came from the water and regenerates the resin.