Cooling towers are structures that contain water and a fan. They are part of centralized air-cooling systems for buildings or industrial processes.
A cooling tower evaporates water to exchange heat with air passing through the tower. The heat and humidity from the water stream raises the air temperature and relative humidity, and the warm, moist air is discharged from the tower.
Legionella are bacteria found in natural water environments and can grow in human-made water systems, such as plumbing, cooling towers, hot tubs, showers and decorative fountains.
Legionella grow best in water that is between 25°C and 50°C, with the fastest growth happening at 38°C. In cooling towers used in air-conditioning and industrial systems, the water temperature is usually between 28°C and 45°C. These temperatures help the bacteria multiply quickly.
Breathing in small droplets or vapour of contaminated water can cause mild infection (Pontiac fever) with flu-like symptoms or pneumonia (Legionnaires’ disease). The elderly and immunocompromised people are at greater risk of illness.
From January 1, 2023 to October 31, 2023, there have been a total of 304 confirmed cases of legionellosis reported in Ontario. More than half of cases required hospitalization with some infections being fatal.
Learn more about Legionellosis.
To reduce the risk of Legionella contamination and protect the health and safety of building occupants and the surrounding community, we encourage you to follow industry best practices/standards for cooling tower maintenance and monitoring.
We periodically send information to cooling tower owners/maintenance operators on cooling tower maintenance best practices. We also maintain an inventory of cooling tower locations in our service area to assist in potential Legionella outbreak investigations.
To notify us of a cooling tower location or to update contact information for a cooling tower, please complete the notification form:
