The group of bacteria most frequently encountered in water distribution systems consists of nonfermentative gram negative rods. Only a small percentage of these bacteria are identifiable using commercially prepared kits or other identification keys because many isolates fail to grow in conventional media used for biochemical characterization. In this study, modified base media were developed and used with specific substrates to detect enzymatic activity. The use of the modified base media combined with a lower incubation temperature allowed expression of increased enzymatic activity by many of the organisms. Although this permitted the characterization of the majority of these organisms, exact identification was unsuccessful since these organisms do not fit descriptions of known species found in current taxonomic schema.