A method for making a low pressure cartridge for liquid filtration, particularly of minerals from drinking water, comprises locating a pair of substantially identical end cap members telescopically on opposing ends of a tubular member. The end cap members are coupled to the tubular member mechanically by interference between four circumferential rings raised from an inner surface of each of the end caps and like numbers of circumferential grooves on a facing surface of the tubular member. O-rings between the telescoped members provide further fluid sealing and increased mechanical coupling, if desired. Different axial spacing between different adjoining pairs of rings assure axial alignment of the end caps with the tubular member during assembly.