An insert for a storm drain or sanitary sewer inlet such as are found in factory or warehouse floors, parking lots and car washes in which the insert holds one or more bags of filter media. The bags have a very open structure such as coarse weave cotton permitting water entering the drain to pass through each bag and the filter media inside the bag. The entire bag may be conveniently withdrawn from the insert and replaced as the filter media becomes saturated. Preferably, a first bag contains an absorbant cellulose particulate media which absorbs oils and greases and post non-volatile hydrocarbons and a second bag contains specially textured activated carbon which absorbs organically bound heavy metals and volatile hydrocarbons as well other VOCs (volatile organic compounds). Various types of filter media and configurations of these media also allows for the removal of dissolved heavy metals, and even the removal of pathogenic microbes. The insert is constructed to permit withdrawing periodically samples of water for analysis. Another embodiment permits controlled periodic inoculation of the filter media in situ with bioremediating microbes to prolong the life of the filter media.