More specifically, the present invention features an improved feeder tube for a water treatment cartridge that provides treatment by a solid compound for a slipstream of untreated water flowing through the cartridge. The feeder tube includes a first end and a second end, such that the slipstream of water generally flows into the feeder tube at the second end and out of the feeder tube at the first end. A bottom plug assembly is in operational relationship with the second end and includes a porous plug being sized and configured to provide filtration and purification for the slipstream portion of the water.