Desalination refers to any of several processes that remove excess salt and other minerals from water. Water is desalinated in order to convert salt water to fresh water so it is suitable for human consumption or irrigation. Sometimes the process produces table salt as a by-product. It is used on many seagoing ships and submarines, and desalination projects/facilities can be found locally on Catalina Island and in San Diego County.

Most of the modern interest in desalination is focused on developing cost-effective ways of providing fresh water for human use in regions where the availability of fresh water is, or is becoming, limited. Desalination is a controversial water supply solution as it is very energy intensive, costly, and can have significant effects on marine life and the environment.