Abstract: A water treatment system includes a main container defining an interior and having an upper edge, a reservoir removably insertable into the interior and located upon the upper edge, the reservoir defining a cartridge seat including a plurality of holes in communication with a helical thread, and an annular landing vertically depending from the thread, a filter cartridge including a cap associated with a sump body and having a filter media in the sump body, the cap having a plurality of radially outwardly projecting pins constructed and arranged for engaging the holes and the helical thread, an annular seal disposed externally on the sump body and spaced below the cap. The filter cartridge and the cartridge seat are configured so that upon the cap pins engaging the helical thread, upon reaching a fully engaged position of the cap in the thread, the seal is compressed against the annular landing.