Reverse osmosis

=== Water and wastewater purification ===
RO-purified rainwater collected from storm drains is used for landscape irrigation and industrial cooling in Los Angeles and other cities.

In industry, RO removes minerals from [[boiler water]] at [[power plant]]s.<ref>{{cite book |editor-last1=Shah |editor-first1=Vishal |title=Emerging Environmental Technologies |date=2008 |publisher=[[Springer Science]] |location=[[Dordrecht]] |isbn=978-1402087868 |page=108 |url=https://books.google.com/books?id=ldeJ713eKPAC&pg=PA108}}</ref> The water is [[distilled]] multiple times to ensure that it does not leave deposits on the machinery or cause corrosion.

RO is used to clean effluent and [[Brackish water|brackish groundwater]]. The effluent in larger volumes (more than 500 m<sup>3</sup>/day) is treated in a [[water treatment plant]] first, and then the effluent runs through RO. This hybrid process reduces treatment cost significantly and lengthens membrane life.

RO can be used for the production of [[deionized water]].<ref>{{cite book|last1=Grabowski|first1=Andrej|title=Electromembrane desalination processes for production of low conductivity water|date=2010|publisher=Logos-Verl.|location=Berlin|isbn=978-3832527143|url=https://books.google.com/books?id=ORVFoMq6HroC&pg=PA2}}</ref>

In 2002, Singapore announced that a process named [[NEWater]] would be a significant part of its water plans. RO would be used to treat wastewater before discharging the effluent into reservoirs.