Deionization is a process which uses specially-manufactured ion exchange resins which bind to and filter out the mineral salts from water. Because the majority of water impurities are dissolved salts, deionization produces a high purity water that is generally similar to distilled water quickly, with less expense, and without scale buildup. However, deionization does not significantly remove uncharged organic molecules, viruses or bacteria, except through "accidental" trapping by the resin. Specially made strong base anion resins can remove Gram-negative bacteria. Deionization can be done continuously using Electrodeionization.

It should be noted that removal of all ions from water is next to impossible, since water self-ionizes quickly to reach equilibrium.