Highly purified water (HPW), high purity water or ultrapure water is necessary for various applications including dialysis, pharmaceutical and electronics. Highly purified water is a commonly used term to emphasize the fact that the water is treated to the highest levels of purity, including the removal of: organic and inorganic compounds; dissolved and particulate matter; volatile and nonvolatile, reactive and inert; hydrophilic and hydrophobic; and dissolved gasses.
Electronics and semiconductor fabrication plants use highly purified water as a cleaning agent and for etching processes, so it is important that the water not contain dissolved contaminants that may precipitate or particles that may lodge on the circuits and cause microchip failures. Several organizations and groups develop and publish standards associated with the production of highly purified water. The most widely used requirements for highly purified water quality for electronics and semiconductor fabrication are documented by the American Society for Testing and Materials International (ASTM International) and Semiconductor Equipment and Materials International (SEMI).