Distillation removes all minerals from water, and the membrane methods of reverse osmosis and nanofiltration remove most, or virtually all, minerals. This results in demineralized water, which has not been proven to be healthier than drinking water. It is required for electroplating,Dialysis, chemical mixing etc.
In general two exchanger can use for DM plant one called Cation exchanger another is Anion exchanger. Both exchanger should remove total Hydronic ion from raw water.