Reverse osmosis (RO) is a water purification technology that uses a semipermeable membrane to remove pathogens (bacteria, viruses); agrochemicals, chloride, organic matter, industrial waste, chemicals, heavy metals, toxins, pesticides, minerals and particles from drinking water. An RO unit is a self-contained water treatment system.
Costs
The cost varies from $50 to $5,000 depending on the quality and capacity of the system. Most people’s needs can be served by a system that costs $150 to $500 (https://www.unce.unr.edu/publications/files/nr/2005/FS0510.pdf)
Evidence of success
Water supply and sanitation project in Sri Lanka involving 800+ schools (http://siteresources.worldbank.org/EXTWAT/Resources/4602122-1213366294492/5106220-1234469721549/36.2_SRI_LANKA.pdf); In Australia, The Rainwater Tanks in Schools project assisted all 22 primary and secondary schools in the Kogarah area to increase the efficiency of water use and install rainwater tanks to reduce potable water use in toilet flushing and irrigating school gardens (https://www.iwra.org/congress/2008/resource/authors/abs636_article.pdf)