A modular filter system is provided with one or more modules that can be interchangeable, depending upon the specific application or specific health or environmental issue presented. Disclosed combinations can include one or more of any of the following modules in any relative position to one another: (a) a microbiological contaminant mitigation module, preferably in the form of an inverted u-shaped hollow fiber filter module wherein the fibers have ends potted on the downstream side and that consists essentially of hydrophilic fibers for water filtration with a small amount of hydrophobic fibers for venting of entrapped air; (b) a first chemical mitigation module, preferably in the form of an adsorption module comprising carbon or the combination of carbon and a deionization resin; and (c) a second chemical mitigation module, preferably in the form of a deionization resin module. Modules including a carbon bed or a resin bed may be equipped with a pair of hydrophobic foam bed restraints that apply opposing axial pressure to the bed in all operating conditions.