Abstract: A self contained water purification process system uses a self cleaning, self sanitizing reverse osmosis unit for reliably producing purified water, storing the water, and distributing it to a central supply piping system while maintaining the integrity of the purified water. Make-up water is prepared for reverse osmosis purification by means of staged conventional filtration and chlorine removal. The prepared make-up water is then fed into one or more reverse osmosis modules by a pump at a high velocity and pressure. About 85 percent of the make-up water exits the module as purified water. All of the water not passing through the reverse osmosis membranes returns to the suction end of the pump where it blends with incoming make-up water except for a small portion that is discharged to a waste drain. The high velocity flow maintains a shear effect within the modules to prevent a sediment deposition and biofilm from occurring on the membranes and increases the efficiency of water usage.