The DOW composite reverse osmosis membrane is composed of three layers, as shown in the following figure. A thin polyamide (PA) layer (around 0.2 micron) deposited on the top of a polysulfone (PS) porous layer (about 50 microns), which is on the top of a polyester (PE) nonwoven fabric support sheet (about 120 microns). Each layer is designed and manufactured according to specific requirements and functions.