http://www.rxdpurewatersystem.....com/di-water-system/ For many applications, water are used as a rinse or ingredient, so the ions are regarded as impurities and must be removed from water. Partial deionized water can be produced on-site for immediate use or purchased in container. But total deionized water can only be produced on-site for immediate use, because total deionized water can be polluted by air or the container, so it cannot be transported or stored. Reverse Osmos