In the spring of 1985, the Metropolitan Water District of Southern California (MWD) converted its method of water supply disinfection from chlorine to chloramines. This change was implemented to prevent the formation of halogenated organics, called trihalomethanes (THMs), and comply with the U.S. Environmental Protection Agency’s maximum contaminant levels for total THMs in potable water. Similar efforts to reduce the formation of THMs are leading other water utilities to look toward chloramines for disinfection.