text: The movement of a pure solvent to equalize solute concentrations on each side of a membrane generates a pressure and this is the `` osmotic pressure . '' Applying an external pressure to reverse the natural flow of pure solvent , thus , is reverse osmosis .
simplified: Reverse osmosis is a separation process that uses pressure to force a solution through a membrane that keeps the solute on one side and lets the pure solvent to go to the other side .