Reverse osmosis (RO) is a separation process that uses pressure to force a solvent through a semi permeable membrane. Impurities in the solvent are excluded, whilst pure solvent passes through the membrane. In other words, it is the process of forcing a solvent from a region of high solute concentration through a semi permeable membrane to a region of low solute concentration by applying a pressure in excess of the osmotic pressure. This is the reverse of the normal osmosis process.

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