Legionella bacterium is commonly found in natural and man made aquatic environments. Legionella bacteria can possibly be found in any municipal water system. Legionella poses a health risk when the bacteria proliferates in warm stagnant water, and if the water is aerosolized and the droplets are inhaled. Legionella generally does not pose a health risk if a person drinks the water. When a person inhales or aspirates droplets containing the legionella bacterium they can get a serious lung infection known as Legionnaires’ disease or an infection known as Pontiac fever. Legionnaires’ disease has symptoms similar to pneumonia and can be fatal; while Pontiac fever is a milder infection that typically gets better without the need for medical intervention.

Small amounts of Legionella bacteria can grow in untreated or stagnant systems and can lead to an outbreak of legionnaires disease. Legionella can be found in both hot and cold water.

There are several elements that can promote the growth of Legionella bacteria in potable water including:

• Stagnant water-the longer water sits in pipelines, the greater the likelihood the residual disinfectant levels dissipate and lead to pathogen proliferation.
• Biofilm- a slimy substance created by bacteria that forms on the inside walls of pipes. It protects legionella from heat and disinfectant and also provides nutrients for their growth and proliferation.
• Water Temperature- legionella grows in water temperatures of 20-45°C and die off at >60°
• Deadlegs- caused by no flow or little used outlets in the system.
• Disinfectant Levels- maintaining constant disinfectant residual levels is paramount to reducing legionella growth throughout the plumbing system.