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3 Proactive Steps to Minimize Legionella Bacteria Growth in Cooling Towers During the Summer Months


The Rules of the City of New York, Chapter 8 Title 24 §8-04(f). Accessed June 27, 2023.


Last week marked the start to Summer, bringing rising temperatures across the country and the need in buildings for comfort cooling. The Summer months trend with having a higher abundance of Legionella bacteria in cooling tower systems in comparison to the other seasons of the year. Figure A shows seasonal variations in percent positivity in cooling towers, from 2019 to 2022




Although the data suggests that rising temperatures can increase risk of Legionella bacteria amplification in cooling tower systems, there are ways to substantially reduce that risk.

3 Proactive Steps to Minimize Legionella Bacteria Growth in Cooling Towers During the Summer Months:

  1. Monitor your cooling tower system’s water quality. Oxidant (chlorine or bromine) levels, pH, temperature, bacteria dip slides, and Legionella bacteria culture samples are all indicators of your cooling tower system’s overall water quality. High dip slide counts and/or positive Legionella bacteria results could indicate the need for an increase in oxidant residual. With the right chemicals and automation, this can quickly be addressed.

  2. Increase the oxidant level in your cooling tower system. A higher-than-normal dosage level of chlorine- or bromine-based biocide can help minimize the risk of Legionella growth in cooling tower systems during the summer months. In fact, the New York City Department of Health and Mental Hygiene requires that all cooling towers receive one summertime hyperhalogenation between July 1 – August 31 each year.[1]

  3. Inspect your equipment. Cooling tower system equipment parts, such as drift eliminators, fill, and basins can all harbor biofilms and scale, allowing Legionella bacteria to amplify. By performing routine inspections on equipment, these findings can be acted upon promptly.

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

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