Legionnaires’ disease is a serious form of pneumonia caused by Legionella bacteria. While it can appear in many types of water systems, one of the most frequently identified sources in large outbreaks is the cooling tower. For building owners, HVAC operators, industrial facilities, and public health professionals, understanding this connection is critical — not only for regulatory compliance, but for protecting human life.
What Is Legionnaires’ Disease?
Legionnaires’ disease is caused by inhaling microscopic water droplets that contain Legionella bacteria. It is not spread person-to-person. The disease can lead to severe pneumonia, hospitalization, and in some cases, death. People over 50, smokers, and those with weakened immune systems are most at risk.
According to the CDC, thousands of cases are reported each year in the United States, but the true number is likely much higher due to underdiagnosis and misidentification.
Why Cooling Towers Are a Major Risk
Cooling towers are a component of HVAC and industrial systems designed to remove heat by dispersing water droplets into the air. This same mechanism — aerosolizing water — creates an ideal pathway for Legionella exposure if the system becomes contaminated.
Several factors make cooling towers particularly vulnerable:
-
Warm water temperatures (77–113°F / 25–45°C): the perfect breeding range for Legionella.
-
Stagnation or low circulation: allows bacteria to multiply.
-
Biofilm, algae, and scale: provide protective environments for bacteria.
-
Organic debris or nutrient buildup: feeds microbial growth.
-
Aerosolization: disperses bacteria-laden droplets over wide areas, sometimes across entire city blocks.
When these factors converge, a contaminated cooling tower can release Legionella into the air where it can be inhaled by people even far from the location.
Notable Outbreaks Linked to Cooling Towers
Many major Legionnaires’ outbreaks globally have been traced back to cooling towers. Public health investigations use environmental testing and DNA markers to match patient samples with water system sources. In numerous cases, improper maintenance, infrequent water treatment, or failing biocide programs were identified as contributing factors.
In 2015, a major outbreak in New York City resulted in more than 120 illnesses and 12 deaths — traced to poorly maintained cooling towers. This event led to new legislation requiring routine inspection, cleaning, and certification of cooling towers.
Prevention: The Role of Proper Water Treatment
The most effective way to control Legionella in cooling towers is through proactive water management, which includes:
-
Routine inspections and documentation
-
Continuous biocide treatment
-
Scale and corrosion control
-
Regular cleaning and disinfection
-
Temperature and pH monitoring
-
Preventing stagnant water conditions
-
Following ASHRAE Standard 188 and CDC guidelines
-
Legionella testing as part of a Water Management Program
Using high-quality water treatment chemicals, filtration systems, and corrosion inhibitors significantly reduces the risk of bacterial growth and equipment failure.
Why Prevention Matters
Beyond human health, Legionella contamination can lead to lawsuits, regulatory penalties, brand damage, expensive system downtime, and emergency remediation. For hospitals, hotels, universities, manufacturing plants, and commercial buildings, prevention is far cheaper and safer than responding to an outbreak.
A well-maintained cooling tower is not just a mechanical system — it is a public health responsibility.
Looking For Cooling Tower Maintenance?
Cooling Tower Products has over 4 decades of experience with cooling tower maintenance and can help you with any cooling tower related project. Contact us today and get the professionals at Cooling Tower products on your side.
