A filtration system is adapted for use and integration with cartridge-based beverage dispensing systems that mix an additive (flavor) with a base liquid (water) as the base liquid is dispensed from a container and through the cartridge. A support frame may support an annular charcoal fabric filter element secured with an end cap and defining an inner cavity to house and surround a portion of the cartridge. A filter cage may enclose the filter element. The support frame may include a bayonet-type connector to secure the filter assembly to a container lid. Base liquid flowing from the container and through the cartridge necessarily flows first through the filter element as a user drinks from the container. Related methods for assembling the filter assembly and installing the filter assembly on a cartridge/lid assembly are also disclosed.