Abstract: A water purification system for home or light commercial application including a preconditioning stage followed by an integrated water sterilization stage. Both stages utilize a single pressure chamber in which the active medium for the preconditioning stage is placed within this chamber as is the entire sterilization stage. More specifically, UV sterilization is contemplated with the UV stage having a stainless steel vessel which, however, is operated at zero differential pressure. A single head is fitted to the top of the pressure chamber and serves multiple functions of admitting the water to be purified and expelling the purified water and, further, to retain the UV vessel, the UV lamp and quartz shield. A segregation device is positioned at the inlet to the UV vessel to separate the respective stages and to assure that none of the preconditioning medium is admitted to the UV vessel.