5 Ways to Manage Legionella Bacteria Risk Caused by Heavy Rains

5 Ways to Manage Legionella Bacteria Risk Caused by Heavy Rains

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

This summer, intense rainfall and flooding have impacted numerous parts of the United States. Studies and advisories have reinforced the impact extreme rainfall and flooding can have on Legionella bacteria proliferation.  Findings from a study released in 2022 suggest that the “increase in Legionnaires’ disease across the US may be explained by flooding…” and that Legionnaires’ disease hospitalizations increased in months with anomalously high precipitation.[1]  A study from 2007 found a correlation between increased rainfall and increased risk of legionellosis by analyzing the association between monthly legionellosis incidence and monthly rainfall totals from January 1990 to December 2003 in five mid-Atlantic states.[2]   

Legionella bacteria is found naturally both in freshwater environments, like lakes, rivers and streams and soil.3  During periods of heavy rainfall and flooding, there are several potential mechanisms that may contribute to the increased risk of legionellosis.[2]  Rainfall and flooding can agitate and release Legionella bacteria- contaminated soils into flood water.  The stagnation that can occur with flooding could then provide conditions that would allow the bacteria to grow and amplify.   

Further, depending on the severity of rainfall or flooding, the drinking water supply may be placed on a boil water advisory.  During a boil water advisory, it is expected that less water will be consumed than during times of normal operation.  This could lead to stagnation in water distribution piping which, in conjunction with loss of disinfectant and disruption of biofilm, may make building water systems more susceptible to Legionella bacteria growth and amplification.   

While these weather-related events can increase the risk of Legionella bacteria amplification fortunately there are some easy ways to significantly minimize risk. Keep reading for actionable ways to protect your water systems during times of extreme weather! 

5 Proactive Steps for Legionella Bacteria Control During Heavy Rainfall and Flooding: 

  1. Increase flushing in your potable water systems: Flushing can aid in reducing biofilms and waterborne pathogens by increasing disinfectant levels and decreasing water age.  CDC and ASHRAE both recommend routine flushing for waterborne pathogen control.[4,5]

  2. Implement control measures when a boil water advisory is lifted: The CDC recommends several actions to implement at your disposal when a boil water advisory is lifted[6]:
    • Flush, clean and sanitize equipment with water line connections per manufacturer’s instructions. 
    • Flush pipes, faucets and drinking water fountains for at least 5 minutes. 
    • Drain and refill hot water heaters set below 113°F 
    • Change all point-of-entry and point-of-use filters, including those associated with equipment that uses water.

  3. Take routine Legionella bacteria samples in your potable water and your cooling tower: By proactively taking routine Legionella bacteria samples, you’ll be able to make immediate adjustments to your facility’s Water Management Program to mitigate risk of legionellosis. Both CDC and ASHRAE recommend routine Legionella bacteria sampling.4,5  Additionally, healthcare facilities in New York State must sample for Legionella bacteria in their potable water systems.7  New York State and New York City have Legionella bacteria sampling requirements for cooling towers, as well.[8]

  4. 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.[9]

  5. Monitor your cooling tower system’s water quality and inspect equipment: 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.  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 Water Management, Inc. can assist your facility with coliform sampling, Legionella bacteria sampling, and cooling tower and ice machine cleanings as proactive measures and validation of these action items at your facility.  Barclay works with third-party CDC ELITE and drinking water-certified labs to provide our customers with coliform, E. Coli, and Legionella bacteria results, along with result interpretation and relevant recommendations.  Contact Barclay now for assistance and scheduling. 

Contact Barclay Water Management, Inc.

Copyright © 2021, Barclay Water Management. All Rights Reserved.