Back to Basics is an article series that highlights important, but possibly overlooked, information facilities management professionals should know.
The recent outbreak of Legionnaires’ disease in New York City led to dozens of hospitalizations and multiple fatalities. This incident is part of a concerning trend. According to the Centers for Disease Control and Prevention (CDC), the number of reported Legionnaires’ disease cases in the United States continued to rise in 2025, with outbreaks often occurring in hospitals, senior living centers, and residential buildings.
Legionnaires’ disease is a severe form of pneumonia caused by Legionella bacteria. In New York City, health officials recently declared the local outbreak over after an investigation that traced the bacteria to cooling towers at a hospital and nearby construction site.
While Legionella bacteria thrive in warm, moist conditions like water heaters, fountains, and more, HVAC cooling towers are among the most common reasons for an outbreak of Legionnaires’ disease.
Why? As Goodway Technologies, a provider of HVAC industrial maintenance solutions, explains, a cooling tower’s function is to re-cool water that has been used in a building’s HVAC cooling system. To accomplish this, it expels heat from the system using evaporative cooling and large fans, reducing the water temperature before sending it back to the chillers for re-cooling. When the tower is not properly maintained and cleaned, the warm water, along with dust, dirt, and debris, becomes a breeding ground for bacterial growth like Legionella. This air-cooling function causes the “drift” of tiny water droplets, which can carry bacteria from the tower, infecting other cooling towers and the surrounding community.
Many facilities managers believe that water treatment with biocides is enough. However, Goodway suggests the outbreak in New York City serves as a stark reminder for facilities managers and contracted maintenance teams of the importance of good water treatment and routine preventive maintenance, including thorough cleaning of their cooling towers.
Goodway recommends the following preventive maintenance steps to reduce the risk of Legionella developing in a facility:
- Inspect Cooling Towers Monthly: Examine all tower surfaces for sediment, scale, and slime, which can build up and help Legionella thrive. Put special focus on cooling tower fill and basins.
- Clean Tower Basin Surfaces Regularly: If there is visible sediment, scale, or slime, then it is time to clean. Using a specialized cooling tower vacuum can make it fast and easy to conduct frequent cleanings without shutting down or draining the system.
- Clean the Fill: The tower fill is a prime environment for scale and bacterial growth. Ensure proper cleaning using a chemical applicator and descaler gel, engineered specifically for cooling towers.
- Treat Circulating Water: Work with a professional water treatment provider to automatically dose water supplies with appropriate biocides at recommended levels, and consider monthly Legionella testing to detect early signs of contamination. Check with local ordinances. Some require monthly, quarterly, or annual inspections.
- Always Disinfect: Regularly disinfect the tower’s surfaces, and before any maintenance is to be performed, use an EPA-registered disinfectant.
“The potential for an outbreak of Legionnaires’ disease increases significantly when routine preventive maintenance is ignored or overlooked,” said Mark Rothenhausen, senior director of sales operations at Goodway. “Facilities managers must remain vigilant and ensure that all systems—especially cooling towers—are properly maintained to reduce risk.”
In addition to reducing the risk of Legionella, proper cooling tower maintenance can lead to significant savings in energy and equipment costs. Clean systems improve the efficiency and longevity of chillers, heat exchangers, and pumps.
“Putting together a maintenance plan and developing proper procedures is no longer optional,” added Rothenhausen. “Taking these steps now can minimize the risks of an outbreak and protect both public health and your bottom line.”
To learn more tips from Goodway, make sure to sign up for the upcoming webinar, “Cooling Tower Maintenance: Why It’s Important and Equipment Needed.” More information and FREE registration are available here.