Membrane filters. Water treatment membranes can perform various functions from mud-water separation, particle separation, brine separation, and ion separation processes. Membrane filtration is a pressure-driven technology that has varying pore sizes from 100 molecular weight to 5 microns. The membrane filter acts as a barrier to separate contaminants from the water by removing the contaminating particles from the water. Reverse osmosis, ultrafiltration and nanofiltration are processes that use a membrane in their filtration process. The RO membrane is effective in blocking salts and inorganic