Main Page | See live article | Alphabetical index Self-ionization of water is when water (2H2O) is dissociated into H3O+ and OH- ions. There is normally a very low percentage of H3O+ and OH- in water. The equilibrium constant for pure water at 25°C is 10-14. Most water is somewhat self-ionized. A water deionizer recombines these naturally occurring ions into pure deionized water, albeit temporarily. This article is from Wikipedia. All text is available under the terms of the GNU Free Documentation License.