The substances that are removed during the water treatment process are suspended solids, viruses, fungi, bacteria, algae, and minerals. The process involves both physical and chemical methods. The chemical used in this process are called water treatment chemicals.

Chemicals that are used are for instance sodium chloride, potassium chloride, citric acid and chlorine dioxide. Chlorine dioxide cleansing serves the removal of organic contaminants on ion exchange resins. Prior to every cleaning treatment resins should be regenerated.