Legionella pneumophila is a motile, rod-shaped, gram-negative, aerobic, bacterium. It is considered to be a "facultative parasite," which in the last twenty years has been identified as the leading cause of Legionnaire's Disease. This disease was first discovered in 1976 among a group of elderly men attending an American Legion Convention in Philadelphia, Pennsylvania¹ (hence the name Legionnaire's Disease). When this outbreak first occurred it shocked the nation and the world, because no one knew why all of the men at the convention were being diagnosed with with acute respiratory failure. However now, more than twenty years later, scientists have learned a great deal about Legionnaire's Disease, as well as the Legionella pneumophila the pathogen which causes it.

Infection by Legionella pneumophila results mainly in Legionnaire's Disease. However, some strains of the bacteria have been known to manifest a disorder called Pontiac Fever. This is a very mild infection which causes influenza-like symptoms and will go away without treatment. Incidence of Legionellosis or Legionnaire's Disease have increased over the past decade or so because of the use of central air conditioning, especially in office buildings, hotels, and hospitals.

Water treatment of cooling towers and industrial systems requires the combination of a number of physical and chemical processes, such as water bleed & replacement, chemical treatment, filtration and pumping. Because the equipment is made by different manufacturers and controlled individually, installation and operation is complicated and inefficient.