3 Ways to Minimize Legionella Bacteria Risk from Cooling Tower Drift

3 Ways to Minimize Legionella Bacteria Risk from Cooling Tower Drift

Image Source: Aaron Lavinsky, Star Tribune

By Hilary Nardone, MPH, Senior Permitting Manager
Certified ASSE 12080 Legionella Water Safety and Management Specialist

Seasonal cooling towers across the United States start up each Spring.  It is critical that cooling towers are cleaned and sanitized every year both for operation efficiency and for public health protection.  Not only do cooling towers produce ideal conditions for Legionella bacteria and biofilm growth, but they also present an acute risk for aerosolization.  This aerosolization is a conduit for Legionella bacteria to drift in a plume from each tower.   In fact, a 2008 study showed that aerosolized plumes from cooling towers have the potential to travel and carry Legionella bacteria for greater than 10 km (over 6 miles).[1] 

A recent 2023 study reinforces this theory.  By creating a predictive model of bioaerosol dispersion using PM10 particles as a proxy, the researchers generated risk maps of Legionella bacteria spread in the surround areas of cooling towers.  The model revealed that the most extensive aerosolization spread is predicted in winter and summer, with an increase in Legionella bacteria risk at a distance of up to 1.5 km from the cooling tower, creating a significant risk of bacteria spread for downwind heavily populated areas.[2] 

Contaminated drift can be minimized by implementing Legionella bacteria mitigation measures in cooling towers.  Below are three ways the bacteria and biofilm growth can be minimized in cooling towers:

3 Ways to Minimize Legionella Bacteria Risk from Cooling Tower Drift:

  1. Apply a disinfection program that includes scale and corrosion inhibitors.

Dosing each cooling tower with a chlorine- or bromine-based biocide can help reduce the growth of Legionella bacteria and biofilms.  Including scale and corrosion inhibitors in your water treatment program can help minimize the amount of mineral deposits in the cooling tower system, thus reducing organic material that would allow Legionella bacteria to multiply.

  1. Test for Legionella bacteria and other water quality parameters.

Regular testing for Legionella bacteria can contribute to improved water management.  Oxidant levels, pH, temperature, bacteria dipslides, and Legionella bacteria samples are all indicators of your cooling tower system’s overall water quality.  Elevated dipslide counts and/or positive Legionella bacteria results could indicate the need for an increase in biocide residual.

  1. Mechanically clean and disinfect each cooling tower.

Thoroughly cleaning and disinfecting a cooling tower’s nozzles, filters, internal components, high-efficiency drift eliminators, and the basin can help control the system’s microbial contamination and increase the system’s efficiency.

Barclay’s team of licensed pesticide applicators apply industry-leading best practices that give peace of mind to cooling tower owners. Contact Barclay Water Management today to ask how Barclay can help you protect your cooling tower from Legionella bacteria amplification.


[1] Nygard K, Werner-Johansen O, Ronsen S., et al.  An outbreak of Legionnaires’ disease caused by long-distance spread from an industrial air scrubber in Sarpsborg, Norway.  Clin Infect. Diseases.  2008; 46(11) 61-69.  doi: 10.1086/524016.

[2] Girolamini L., Brattich E., Marino F., et. al.  Cooling towers influence in an urban environment: A predictive model to control and prevent Legionella risk and Legionellosis events.  Build. Environ.  2023; 228.  doi: 10.1016/j/buildenv.2022.109891

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