Legionella bacteria are found naturally in the environment, usually in water, including hot water tanks, air conditioning cooling towers, humidifiers, whirlpools, spas, hot tubs, and decorative fountains.
Exposure to Legionella bacteria can occur through breathing in small droplets of water in the air that have been contaminated with the bacteria. The bacteria are not spread from person-to-person and you cannot become infected by drinking water containing Legionella bacteria. For more information on the disease, see our Legionellosis Fact Sheet.
There is evidence that water heaters and HVAC (heating, ventilation, air conditioning) systems provide optimal environments for the growth of Legionella bacteria. Regular maintenance of these systems, in accordance with best practices, can help prevention outbreaks of legionella-related illness.
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