Desalination of both seawater and brackish groundwater has been increasing along the coast of southern California, USA. Since 1999, three facilities have been planned, opened, or expanded in order to improve the reliability of supplying municipal water. Since about 1945, most municipal water used in southern California has been imported from sources many hundreds of kilometres away—either from Owens Valley, northern California, or the Colorado River. In the past 20 years, however, these sources have become less reliable because of environmental restrictions and climate variability. In order to continue to ensure an adequate supply of municipal water for the huge population of southern California, water agencies have instituted a variety of measures including conservation, in lieu water trades, new reservoirs, enhanced recharge, and expanded use of desalination. These three desalination facilities illustrate the range of technical options that are being pursued.