Abstract: A combination bottle cap and filter cartridge for use with a reservoir water bottle includes an outer sidewall having a generally cylindrical configuration and an end wall joined to the outer edge of the sidewall. The sidewall is dimensioned to be received about the mouth and neck of the bottle. A cylindrical filter cartridge extends from the cap end wall and is disposed concentrically within the sidewall. The filter cartridge includes an inner end wall disposed within the bottle neck, and a curved inner panel extends from the inner end wall to the cap end wall to define two chambers within the cartridge. A filter chamber contains a charge of granulated filter medium. A plurality of holes are formed in the inner end wall and the cap end wall to admit water from the bottle to the filter cartridge and discharge water therefrom, respectively. A pair of fiber scrims are interposed in the filter chamber between the inner and outer end walls and the filter medium to retain the granulated particles therein.