Backwashing reverse-osmosis and ultrafiltration membranes by electro-osmosis

A process for improving the efficiency of a reverse osmosis process for purification of saline water, said reverse osmosis process consisting essentially of applying to said saline water a pressure in excess of the osmotic pressure of the saline water, said saline water being separated from purified product water by a reverse osmosis membrane whereby pure water is caused to permeate through said membrane while salt molecules are retained by the membrane, comprising backwashing the membrane by application of an electric potential across the membrane to cause an electroosmotic backflow of water through the membrane.