Abstract: A compression sealed bacteriostatic purification and filtration system canister for the treatment of water and other piped liquids which includes a plurality of sequential granular filtering media beds separately contained within respective sections of the canister. The canister walls have molded internal grooves to prevent channeling and to hold section separators; the structural filter separators are highly porous semi-rigid discs, and snap into the grooves. The cylindrical sections increase in diameter in the direction of liquid flow. The sections are axially stacked within the canister. Liquid is admitted at the top end of the pressure vessel tank canister, runs down through the series of sections, and then returns to the canister top to exit through an axial riser tube. The tank canister has a screw-on compression sealed cap which contains fluid inlet and outlet pressurized disconnect couplings to allow leak-free back flushing.