Reverse osmosis (RO) is a common process for purifying or desalinating contaminated water by forcing it through a semipermeable membrane. This technology creates pure water by applying pressure to move water through a membrane, expelling impurities, salts, and other contaminants from the water. The pore size of the reverse osmosis membrane is extremely small, usually about 0.0001 micron, and can effectively filter out small impurities.