A water treatment system having modular-filter based residential reverse osmosis (RO) system that passes a stream of purified water through an ultraviolet light (UV) filter twice to ensure the water is sterile, while using only one UV filter, thereby forcing the water through a UV filter twice in a modular-filter based RO system. The water treatment system also includes a system whereby water passes through the UV filter at both points using only one UV filter by employing a system whereby a purified water stream is passed through a single remineralization module twice. The present invention also includes the method for treating water through such double forced sterilization system.