Just Because Everyone Does It, Doesn’t Mean They Should
Before the 2012 London Olympics, U.S. swimmers Ryan Lochte and Michael Phelps openly admitted to peeing in the pool. Phelps shrugged, “I think everybody pees in the pool,” while Lochte chimed in, “There’s just something about getting into chlorine water that you just automatically go.” Phelps even reassured fans by claiming, “Chlorine kills it, so it’s not bad.”
Well, not quite. Despite the swimmers’ world-class credentials, these Olympians are mistaken. Research published in Environmental Science & Technology Letters reveals that when urine—particularly its nitrogen-based compounds like urea—mixes with chlorine, it produces harmful chemical byproducts. In high enough concentrations, these byproducts may even pose health risks to all pool-goers.
The Gross (and Harmful) Chemistry
When urine mixes with chlorine in pool water, it doesn’t just vanish—it reacts. Two notable chemical byproducts of this reaction are trichloramine (NCl₃) and cyanogen chloride (CNCl). Cyanogen chloride is a toxic compound that can affect the lungs, heart, and central nervous system. Meanwhile, trichloramine is known to irritate and damage lung tissue and repeated exposure to it may cause asthma-like symptoms, especially in frequent swimmers and pool workers.
These concerning findings have prompted researchers like Dr. Xing-Fang Li, a Canada Research Chair in Analytical and Environmental Toxicology at the University of Alberta, and Dr. Lindsay Blackstock, an Assistant Teaching Professor at Thompson Rivers University with a PhD in Analytical and Environmental Toxicology, to explore better ways to monitor pool water quality and raise awareness about the importance of proper pool hygiene. Their research highlights the importance of swimmers practicing good hygiene, such as showering before entering the pool and avoiding urination in the water, to maintain a safe swimming environment.
What Research Reveals
In one of the most cringe-worthy studies of recent years, those same researchers found that the average public swimming pool contains about 75 liters (or roughly 20 gallons) of human urine. As lead author Dr. Lindsay Blackstock (aforementioned) bluntly put it, this confirms that “people are indeed urinating in public pools and hot tubs.”
To make this stomach-turning estimate, the research team first needed to identify a reliable marker that shows up consistently in human urine. They landed on acesulfame potassium (ACE)—an artificial sweetener used in everything from diet sodas to baked goods. ACE is popular, chemically stable, and, crucially, not metabolized by the body. That means it passes right through and exits in urine, making it an ideal tracer for the study.
Armed with this target, the researchers analyzed 250 water samples from 31 actively used swimming pools and hot tubs in two Canadian cities, as well as 90 samples of tap water for comparison.
The results? Concentrations of ACE in the pool and hot tub samples ranged from 30 to 7,110 nanograms per liter—on average, 570 times higher than the levels found in tap water. From this data, researchers estimated that swimmers release an average of 7 gallons of urine into a 110,000-gallon pool. In a pool, twice that size—220,000 gallons—that figure climbs to 20 gallons of pee.
In Conclusion: Think Before You Sink
The next time your eyes are burning and you start coughing at the community pool, it might not be the chlorine’s fault—it could be someone’s soda-sweetened pee reacting with disinfectants. As Dr. Blackstock gently reminds us, “Be considerate to others and make sure to exit the pool to use the restroom when nature calls.” (Yes, that means you, Olympic hopeful).
This study is also a splashy reminder that health risks can lurk in the most unexpected places—even in an activity as wholesome as swimming. So while you should still hit the pool for your cardio, maybe do it with goggles, a nose clip, and, most importantly, good insurance.
Unexpected health issues can pop up anywhere. Make sure you are covered. Contact a licensed insurance agent today to find a plan that helps keep you afloat—no matter what life (or the pool) throws at you.
And remember, swimming is not just a summertime thing, which means year-round awareness is key. One other habit that should stick with you every season? Sunscreen. Believe it or not, damaging UV exposure can still reach you through car windows, cloudy skies, and minute-long outdoor errands. To learn why daily SPF matters (and what happens when you skip it), check out our article, Revisiting Sunscreen.
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This article was updated on June 4, 2025.