Many different bacteria species may appear in industrial water systems. Control, therefore, becomes extremely difficult because agents toxic to one species may have little effect on another. Bacteria may exist as single cells or multicellular colonies. In deference to the variety of species, they are categorized by physical and metabolic characteristics. The following table denotes some of those categories.

A partial list of some common bacterial types found in industrial water systems appears in Table below. This list is not all-inclusive, but is presented to show representative examples of the bacterial population, their characteristics and problems they cause in industrial water systems.