There are two sources that provide Riyadh City with potable water: 1. Desalinated seawater from Al Jubail plants pumped from Saudi Arabia＇s East Coast. (represents about 60%). 2. Brackish water from deep and shallow wells, which are primarily treated by eight plants of which six are, followed by reverse osmosis desalination plants. (represents about 40%). Among the six RO plants supplying Riyadh are Manfouha plants (1 & 2). While receiving raw water from deep wells, the two plants are designed to produce about 84,000 m(3)/day. The Manfouha RO plants were commissioned starting in 1984 and are still operating at close to design capacity. The two plants are presently operated and maintained by Riyadh Water and Sewage Authority. This paper covers plant design parameters of Manfouha plants, while high lighting membranes performance after more than ten years of operation.