A variety of aquatic bacteria were isolated and tested for their ability to degrade humic substances and their aromatic residues/monomers which serve as precursors of the trihalomethanes (THMs) found in chlorinated drinking waters. The majority of them were Gram-negative, oxidative types dominated by pseudomonads. Most of the 146 isolates were found to utilize as their sole source of carbon several or more of ten aromatic compounds known to be products of degradation of humus and also to be precursors of THMs. The aromatics tested, with percent of the isolates utilizing the compound in parentheses, were: p-hydroxybenzoate (49), vanillic acid (48), 3,5-dihydroxybenzoic acid (16), syringic acid (19), vanillin (30), benzoic acid (27), ferulic acid (34), resorcinol (9), catechol (8) and protocatechuic acid (27).