Legionella is bacteria commonly found naturally in freshwater, such as lakes, rivers, ponds, and streams, generally at levels too low to cause disease in people. However, certain conditions that may be present in buildings and homes promote the growth of the bacteria. When water is contaminated with larger quantities of Legionella, it gets released into the air in the form of droplets or mist, the primary route of transmission. The key to preventing outbreaks of Legionnaires’ disease is to control Legionella bacterial growth in water systems through preventive maintenance.