The article presents an animal identification guide designed for water utility personnel to identify aquatic animals they may find in connection with their work. This guide identifies an organism as a moss animal or a sponge, or a segmented worm or a roundworm. These animals are not associated with human diseases. They do, however, cause nuisances because of their great abundance in raw‐water sources, water treatment installations, finished‐water reservoirs or distribution systems. More commonly, they are seen during casual microscopic examination and have stimulated questions about their names and origins. The article provides a list of other published resources for animal identification. The article provides a classification of the 25 animals most common in potable water supplies; 23 additional animals associated with such supplies are listed by name only under their appropriate general classification categories. Drawings are provided of each animal.