Reverse osmosis is a technique for purifying which substance?

Reverse osmosis is one of the processes that makes desalination (or removing salt from seawater) possible. Beyond that, reverse osmosis is used for recycling, wastewater treatment, and can even produce energy.

It was only in the 1950s when researchers began exploring how to desalinate ocean water that reverse osmosis was brought up as a possibility. They found that applying pressure to the saltwater side could work to produce more fresh water, but the amount they created was extremely small and not useful on any practical scale.

A much more advanced filter was created by two scientists. The hand-cast membranes made from cellular acetate (a polymer used in photograph film) allowed larger quantities of water to move through much faster, and the first reverse osmosis desalination plant began running a small scale operation in Coalinga, California in 1965.