To give this some perspective, CDC estimates that pools in the U.S. have 301 million swimmer visits per year. Given this figure, the model would predict the following (compared to what is currently being seen above).
Using the assumptions within the model that determine the proposed 20:1 ratio, and assuming there was no trace of chlorine during an outbreak, the incidence of Giardia is overestimated by more than 15 million cases per year. Similarly, the model overestimates the incidence of E. coli by more than 100,000 cases.
When looking at the model’s prediction for pools that were run at the highest ratio of CYA and FC that fits with the current recommendations of 1 ppm FC and 100 ppm of CYA, there should be more than 750,000 cases of Giardia coming from those pools each year. How many have actually been observed from pools that were confirmed to have 1 ppm of FC? None! That said, how confident can the industry be in changing decades of water treatment practices—methods that are demonstrated to effectively prevent illnesses due to pathogens susceptible to chlorine—based on a model that so severely overestimates the scope of the problem?
Conclusion
The key takeaway from this—where both model and real-world experiences agree—is the most important factor in keeping a clean, healthy swimming environment is proper pool maintenance, and keeping a chlorine residual of 1-4 ppm. Cyanuric acid helps prevent sunlight from destroying that residual, which makes it easier and less expensive for pool operators to maintain the appropriate chlorine level. That said, it needs to be asked, who is behind the continuous push to further regulate cyanuric acid in the industry? If the industry is truly concerned about public health, the focus needs to be on maintaining recommended levels of free chlorine to prevent disease from the readily controlled pathogens and on using secondary disinfection systems and proper maintenance practices to combat Crypto outbreaks. Rather than swimming in spreadsheets, it is the aquatic industry’s responsibility to ensure bathers are swimming in clean and clear pool water.
Roy Vore is a technology manager at BioLab Inc. His work focuses on the control of microbial growth in recreational water and household surfaces. He is a Certified Pool & Spa Operator (CPO), a member of the National Swimming Pool Foundation’s (NSPF’s) education committee, an active contributor to the Pool & Hot Tub Alliance’s (PHTA’s) Recreational Water Quality Committee, was a major contributor to the Disinfection Water Quality module of the Model Aquatic Health Code (MAHC), and the lead author of the National Swimming Pool Foundation’s (NSPF’s) Recreational Water Illness handbook. Vore holds a PhD in bacterial physiology, and masters and bachelor’s degrees in microbiology. He has written more than 80 scholarly papers and presentations on the selection and use of industrial biocides, biocide testing methodology, the microbiological of pools and spas, and the governmental regulation of biocides. He can be reached via e-mail at roy.vore@biolabinc.com.
Jeffrey Gaulding received his PhD in chemistry from Georgia Tech and his bachelor of science from Emory University. During his doctoral work he was awarded several fellowships, including being appointed to a National Institutes of Health training grant. Gaulding began his career in the pharmaceutical industry and has been working in the pool and spa industry for several years. He is also a Certified Pool & Spa Operator (CPO) and recently joined the Pool & Hot Tub Alliance’s (PHTA’s) Recreational Water Quality Committee. Gaulding can be reached via e-mail at jeff.gaulding@biolabinc.com.
References
Centers for Disease Control and Prevention (CDC). 2018. “Outbreaks Associated with Treated Recreational Water”—United States, 2000–2014. Morbidity and Mortality Weekly Report (MMWR), 67, 547-551.
