Legionella are bacteria occuring in soil and aquatic environments. It can infect your body through inhalation of contaminated water droplets and leads to Legionnaires’ Disease (potentially-fatal bacterial lung infection). Legionella can spread in human-made water systems like pools, cooling towers, air conditionning, showers, faucets, fountains, hot water tanks. At low temperatures (under 68°F) the bacteria can survive but not proliferate, over 140°F the bacteria dies.