A filter/sanitizer has a filter housing, provided with a fluid inlet and a fluid outlet, a filter cartridge with a hollow interior, located within the filter housing, and a sanitizer cartridge, with a hollow core, positioned within the hollow interior of the filter cartridge. In a preferred embodiment, the sanitizer cartridge is constructed with an outer fluid-permeable member and an inner fluid-permeable member, the outer and inner members substantially enveloping a space therebetween, with the space containing a sanitizing media bed. In operation, as fluid enters the filter housing through the fluid inlet, substantially the full flow of fluid passes through the filter cartridge, through the sanitizer cartridge and around the sanitizing media contained within the bed, into the hollow core of the sanitizer cartridge, and out of the filter housing through the fluid outlet.