Brackish Water Reverse Osmosis (BWRO): The membranes used for reverse osmosis have a dense barrier layer in the polymer matrix where most separation occurs. This process requires that a high pressure be exerted on the high concentration side of the membrane, usually 2–17 bar (30–250 psi) for fresh and brackish water but it has also been used to purify fresh water for medical, industrial and domestic applications since the early seventies.