Some embodiments provide a water filtration system that is fluidly coupled to a water feed line and/or a water supply line and is designed to filter contaminates from the water supply. The water filtration system includes an outer housing, a front cover, a rear cover, a pump, a reverse osmosis (RO) element, a pre-filter cartridge, a post-filter cartridge, a permeate flush tank, a RO manifold, and a sensor manifold. The water filtration system further includes a pump and at least one solenoid. When assembled, a RO housing, a pre-filter housing, and a post-filter housing surround the RO element, the pre-filter cartridge, and the post-filter cartridge, respectively. The filter cartridges hold replaceable filtration media in an interior cavity and contaminants and other impurities are removed as water flows through the filtration media of the filter cartridges.