Protecting Swimming Pools and Hot Tubs from Legionella Bacteria and Other Waterborne Pathogens

By Hilary Nardone, Environmental Group Training Manager
Certified ASSE 12080 Legionella Water Safety and Management Specialist

One aspect of summer that is ubiquitous among vacationers and “stay-cationers” alike is the use of swimming pools and hot tubs.  Although relaxing to visit, if recreational water sources are not properly treated, they can be sources of dangerous waterborne opportunistic pathogens.

A study recently published in the CDC’s Morbidity and Mortality Weekly Report (MMWR) found that there were 208 outbreaks associated with treated recreational water reported to the CDC between 2015 – 2019, 96 percent of which were associated with public pools, hot tubs, or water playgrounds.[1] Of the 208 outbreaks, 71 were associated with hotels and 65 were caused by Legionella bacteria, resulting in 13 deaths.  Most outbreaks were reported in the summer months, as pictured in Figure 1 below.

Hlavsa MC, Aluko SK, Miller AD, Person J, Gerdes ME, et. al. Outbreaks Associated with Treated Recreational Water – United States, 2015 – 2019. MMWR. May 21, 2021; 70(20):733-738.

It is therefore necessary to ensure that public pools, hot tubs, and spas are properly treated to minimize the risk of potentially harmful opportunistic waterborne pathogens, particularly during summer months.  The CDC’s Model Aquatic Health Code (MAHC) “represents a collaboration among local, state, and federal public health officials…to optimize prevention of illness and injury associated with public aquatic venues…”[2] Currently in its 3rd edition, the MAHC outlines preventative guidance for operating, maintaining, and disinfecting treated recreational water sources.  A fourth edition is expected later this year.

Many public pools are re-opening this summer after a prolonged shutdown due to the COVID-19 pandemic.  As stagnant water conditions cause the buildup of biofilms which can contribute to the amplification of these bacteria, it is therefore even more essential to minimize this risk of Legionella bacteria and other waterborne pathogens.  In addition to complying with federal, state, and local guidelines, proper cleaning and disinfecting and overall operational maintenance can help to ensure a safe environment for swimmers and bathers.[3] Developing a Water Management Program for these water sources that considers ASHRAE Standard 188-2021, ASHRAE Guideline 12-2023, the CDC’s Toolkit for Controlling Legionella in Common Sources of Exposure, as well as the CDC’s Toolkit: Developing a Water Management Program to Reduce Legionella Growth and Spread in Buildings will also help mitigate the risk of Legionella bacteria.

Barclay Water Management, Inc. has developed Water Management Programs for recreational water sources and is an industry leader in offering sampling and testing programs to detect Legionella bacteria in both non-potable and potable water systems.  Barclay also has Certified Pool Operators on staff who have first-hand knowledge of recreational water operations and cleaning and disinfection best practices, and can assist our customers with complying with federal, state, and local guidelines.

Be sure to check out our previous blog post on why the number of Legionnaires’ disease cases is higher in the summer months.


[1] Hlavsa MC, Aluko SK, Miller AD, Person J, Gerdes ME, et. al.  Outbreaks Associated with Treated Recreational Water – United States, 2015 – 2019.  MMWR.  May 21, 2021; 70(20):733-738.  https://www.cdc.gov/mmwr/volumes/70/wr/mm7020a1.htm?s_cid=mm7020a1_x.  Accessed July 8, 2021.

[2] Hlavsa MC, Laco JP, Hill VR, Sheehan PA.  2021 Model Aquatic Health Code (4th Edition).  Journal of Environmental Health.  May 2021; 83(9):30-31.

[3] CDC.  Health Swimming: Extended Hot Tub/Spa Closures.  CDC.  https://www.cdc.gov/healthywater/swimming/aquatics-professionals/extended-hot-tub-closures.html Updated July 12, 2021.  Accessed July 20, 2021.

[4] New Model Aquatic Health Code, https://www.cdc.gov/mahc/pdf/2023-MAHC-508.pdf

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