Abstract: A static screen used upstream of a membrane assembly within a water treatment system has a screening surface with a number of openings distributed over its area. Liquid flows through the screening surface to reach the membrane assembly. Various shapes of screening surfaces are described including three-dimensional bodies with openings at or near their lower ends. Methods for cleaning the screen are described including aeration, backwashing and lowering down the water level in an upstream section by partially or completely draining a tank. Various treatment systems or process designs incorporating the screen are described. Screen elements may be made in two or more parts comprising a supporting structure and a separation layer and may be mounted on a conduit or pan.