Legionella bacteria thrive in warm water temperatures between 25°C to 45°C (77°F to 113°F). Temperatures above 50°C (122°F) can be lethal to Legionella, while temperatures below 20°C (68°F) can inhibit growth. In irrigation systems near HVAC equipment, it’s essential to maintain temperatures outside of this ideal growth range to minimize the risk of Legionella proliferation. Regular temperature monitoring and control measures, such as insulation and temperature sensors, can help achieve this goal.