"Legionella is an aquatic bacteria that thrives in warm water environments, and is the cause of Legionnaires Disease. It is commonly found in potable water supplies, hot tubs, cooling towers, fountains, swimming pools, etc. and multiplies in warm conditions especially between 68 – 122 °F. The Legionella bacteria can spread to humans when breathed in."
Hot Water Heater Safety & Temperature: Legionella Prevention