From Water Treatment
RO technology is used to remove dissolved impurities from water through the use of a semi-permeable membrane. RO involves the reversal of flow through a membrane from a high salinity, or concentrated, solution to the high purity, or 'permeate', stream on the opposite side of the membrane. Pressure is used as the driving force for the separation. The applied pressure must be in excess of the osmotic pressure of the dissolved contaminants to allow flow across the membrane.