- ASHRAE Standard 188-2021: Legionellosis: Risk Management for Building Water Systems | ASHRAE Bookstore
- ASHRAE Guideline 12-2023: Managing the Risk of Legionellosis Associated with Building Water Systems | ASHRAE Bookstore
- Controlling Legionella in Cooling Towers | Centers for Disease Control and Prevention
- NSF P453-2017 Cooling Towers - treatment, operation, and maintenance to prevent Legionnaire's disease | ASHRAE Bookstore
- Standard MD 15161 - 2013: Control of Legionella in Mechanical Systems | Public Works and Government Services Canada
Legionella and Cooling Towers
Legionella is a type of waterborne bacteria that can cause illness in humans. It causes two distinct conditions: Legionnaires’ disease (a severe, serious illness) and and Pontiac fever (a milder, flu-like infection).
The bacteria thrive in warm, stagnant water, particularly where dirt, scale, or biofilm (slime) are present.
Hot weather places a significant strain on cooling tower systems, forcing them to operate under increased workloads that reduce efficiency and elevate the risk of mechanical issues. As a result, warm, stagnant, or dirty water creates the ideal environment for the rapid growth of Legionella bacteria.
Most Legionnaires’ disease outbreaks originate in large, complex water systems, such as those found in hotels, apartment complexes, long-term care facilities, and factories. Cooling towers and central air conditioning systems are the most common sources of exposure. Other sources of exposure include hot tubs, whirlpool baths and decorative fountains. People contract the illness by inhaling microscopic water droplets or mist contaminated with the bacteria.
If you are responsible for any of the above possible sources of exposure (i.e., building manager/maintenance), proactive preparation is key to protecting your building and its occupants.
Reducing the risks
Work with your water management team and use this checklist to minimize risks during extreme heat:
- Plan ahead - monitor weather forecasts closely to anticipate and prepare for periods of high heat and humidity.
- Verify water treatment - ensure chemical supplies are adequate and consult your water treatment provider about necessary adjustments for hot weather.
- Inspect equipment - audit your cooling tower and connected components (such as pumps and chillers) to ensure peak operational efficiency.
- Monitor aggressively - increase system surveillance during heat waves. You may need to boost chemical treatments to stop bacterial growth; taking quick action prevents equipment damage, breakdowns, and health hazards.
- Optimize energy use - lower energy costs and reduce grid strain during peak heat times by raising thermostats and limiting non-essential power consumption where possible.