A method for water treatment prior to reverse osmosis

A method for the treatment of feed water with a microfiltration or ultrafiltration membrane unit and a downstream in the flow direction reverse osmosis unit. An aluminum salt coagulant is added to the feed water stream, and at a location upstream of membrane separation unit. The aluminum salt coagulant is added upstream of the membrane separation unit. A sufficient amount of the aluminum salt coagulant is mixed with the feed water in order to obtain a sufficient residence time to control the concentration of aluminum in the discharged from the membrane separation unit permeate.