In the Reverse Osmosis process, water from a pressurized saline solution is separated from the dissolved salts by flowing through a water-permeable membrane. The permeate (the liquid flowing through the membrane) is encouraged to flow through the membrane by the pressure differential created between the pressurized feedwater and the product water, which is at near-atmospheric pressure. The backwash is minimal and the permeated water preserves balanced minerals.
The video above shows a Wastewater Treatment Plant that turns wastewater into potable water. Through the use of Multimedia Tank Filtration the solid biological waste is separated and then enters the Ultrafiltration phase through Reverse Osmosis. (Mobile view unsupported).