Reverse osmosis is one of the finest filtration available today. Reverse osmosis is the process of forcing a solvent from a region of high solute concentration through a semi permeable membrane to a region of low solute concentration by applying a pressure in excess of the osmotic pressure.

In most cases the membranes are designed to allow only water to pass through this dense layer while preventing the passage of solutes (such as salt ions) generated from the industrial processes.

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, and 40 - 70 bar (600 - 1000 psi) for seawater, which has around 24 bar (350 psi) natural osmotic pressure that must be overcome.