A gravity-driven fluid (water) treatment device that includes a bottom portion having at least one treated fluid outlet, an upper perimeter, and a bottom portion side wall that defines an interior volume of the bottom portion and wherein the bottom portion side wall is a shaped surface that is configured to frictionally engage a plurality of differently sized fluid vessel openings and still allow treated fluid to be delivered to the interior of a fluid vessel through the at least one treated fluid outlets; a fluid treatment medium positioned within a fluid filter; and a top portion with an interior volume defined by at least one wall. The fluid filter, the bottom portion and the top portion are each configured to be removably engaged and disengaged to allow for replacement of the filter and reassembly of the overall gravity filter assembly by hand and without the use of tools.