We’re Asking Chlorine to Do A Lot of Heavy Lifting—And It’s Not Up to the Job

You’re midway through your swim set when you realize that giant bottle of water you drank on your way to the pool has caught up to you. You’ve got to pee—bad. What do you do: Get out of the water for a bathroom break, or treat the pool like your own personal toilet?

Peeing in the pool is one of those things generally accepted as something “everyone” does. The sentiment seems to be that it’s no big deal—even Olympic swimmer Michael Phelps once said it’s just a normal part of being a swimmer. “Chlorine kills it, so it’s not bad,” he said, leading epidemiologists everywhere to throw up their hands in frustration.

“A lot of people reference Phelps, saying, ‘Well, he said it’s OK to pee in the pool, and he’s the greatest swimmer ever, so he must know what he’s talking about,’” said Ian Young, epidemiology researcher at Toronto Metropolitan University. “But that’s not the case.”

The myth of “chlorine kills it”

Peeing in the pool isn’t just a discourteous thing to do, it’s also a health hazard. For starters, chlorine doesn’t kill urine as well as most people assume. In a 2017 study of 31 pools and hot tubs, researchers found evidence of urine in every single body of water, despite disinfection methods like chlorine. Most people wouldn’t voluntarily come into contact with someone else’s pee—yet that’s more or less what’s happening when you dive in. But since urine is technically sterile, the yellow stuff itself isn’t where the health hazard lies. It’s what happens when it mixes with the pool water.

When urine comes into contact with chlorine disinfectant, a chemical reaction occurs, yielding volatile and irritating N-Cl-amines. In fact, the scent most people associate with pools is not actually chlorine, but the chemical byproducts of chlorine’s reaction with bodily fluids, including sweat, body oils, and urine. The more chlorine comes in contact with these fluids, the weaker it becomes at doing its job, and the more chemical reactions are released into the water (and the stronger the “chlorine smell” in the pool environment).

“These disinfection byproducts can be hazardous to bathers [swimmers] as well as pool staff like lifeguards,” Young explained. “They can accumulate in the water or even as sort of aerosols above the water, and they can get inhaled. Some people experience effects right away, like eye or throat irritations, coughing, that kind of thing. There’s some evidence that long-term exposure, if you’re in a pool environment for many years and have been exposed to these chemicals, that could have other kind of long-term negative effects, like asthma.”

It’s also important to note that urine isn’t the only thing lurking in the water. Cryptosporidium, a chlorine-resistant microscopic parasite that causes diarrhea, is the number-one cause of recreational water illness. The cause? People not showering to remove fecal matter before they enter the pool. In fact, more than half of Americans report using a swimming pool as what the Water Quality and Health Council describes as “a communal bathtub, either swimming as a substitute for showering or using the pool to rinse off after exercise or yardwork.”

In short, we’re asking chlorine to do a lot of heavy lifting—and it’s not up to the task.

RELATED: Indoor Pools: What’s Really Lurking in the Water?

How many people actually pee in the pool – and why?

So does everyone really pee in the pool, as so many believe? It’s hard to say for sure. About 40% of American adults willingly admit to urinating in the pool in surveys, but experts caution those numbers might be low. After all, when you ask someone about taboo behaviors, even those openly endorsed by Michael Phelps, chances are high they won’t admit to doing something unsavory.

But Young has no interest in finding out how many people actually pee in the pool. As someone who works in public health, he’s much more interested in how to get people to stop (whether they admit to it or not). His 2022 study, Determinants of bather hygiene in public swimming pools: a mixed-methods analysis of online discussion comments, looked at the general sentiment about the behavior.

“We wanted to know what people believed, what people were saying about health-related behaviors with respect to swimming,” Young said. “How do we raise awareness about some of the health risks and preventative measures that people can take to prevent getting an illness from those pool settings?”

Instead of conducting interviews or using a survey, Young and colleagues conducted an observational study of online forums like Reddit and social media platforms where people were discussing the topic of peeing in the pool. “It’s effectively anonymous,” Young said. “And people might be more willing to be truthful about their actual behaviors, especially for odd behaviors where they don’t want to be seen as that person who is peeing in the pool or whatever.”

What the researchers found is that most people aren’t aware of how urine contributes to disinfection byproducts, nor the health hazards that can result. “They didn’t realize that they, as well as other users of the pool, were at risk from this behavior,” Young said. “And because of that, there really weren’t too many negative attitudes about peeing in the pool.”

The Michael Phelps effect also came up repeatedly in online discussions about the practice, noted Young. “We see this all the time in health research, that celebrities can kind of have incorrect advice that has a big influence on people’s behaviors.”

But the biggest surprise for the researchers was that many of the attitudes and behaviors of swimmers are shaped by peer pressure. “The influence of other swimmers was surprising,” said Young. “That swim team environment where people felt that peeing in the pool was, in a way, conforming to social pressures. So if you got out of the pool to pee during a swim practice or something, then you’re not tough enough to actually swim. It’s a sign of weakness, basically. That kind of social pressure came through quite strongly. People also talked about how their coach would be very unforgiving, or they would expect them not to get out of the pool during the middle of a practice. A lot of people with a competitive swim background did say that was a big driver of their behaviors.”

But seriously, stop peeing in the pool

Knowing why people engage in certain behaviors, as Young’s study looked at, is the first step in getting people to change. Though public pools are required to post signs asking people to shower before entering the pool and to get out and use the restroom facilities if nature calls, it’s clear people aren’t actually doing those things consistently. Is it time to employ more drastic measures, such as the mythical “red dye” that supposedly changes the color of pool water when it comes into contact with urine?

“A lot of people mention that,” Young said. “They’re told about that dye as a child to be discouraged, but that doesn’t actually exist. And besides, I don’t think the shaming approach is the way to go.”

Instead, Young encourages better education for swimmers to raise awareness of the consequences of why people shouldn’t pee in the pool. “It’s a general courtesy, yes, but there’s more to it. As a patron of that facility, you want to do your part to make sure the water is clean and healthy. That includes pushing back on cultures where people normalize or even pressure people into engaging in unhealthy practices.”

Young also stresses the need for pool facilities to properly manage their pool filtration and disinfection systems as part of a joint effort for water quality, as well as providing more education and awareness for swimmers about why those signs are posted asking people to engage in hygienic practices.

“Common courtesy isn’t always common,” Young said. “But by talking about this, people can understand why it’s important. That’s where you’re swimming, and you want to keep the highest quality of water possible for yourself and for other bathers.”