Is Peeing in the Pool Really All That Bad?

Besides being downright disgusting, there’s a more dangerous downside to peeing in the pool. (Photo: Flickr/Wade Morgen)

There’s no chemical that will change color — and blow your spot — if you pee in the pool. And doing so is pretty common: Nearly one in five American admits to relieving themselves in a swimming pool, according to a recent Water Quality and Healthy Council survey.

Even the pros do it — when a TMZ reporter asked Olympic swimmer Michael Phelps if he urinated in the water during races, he candidly replied, “Everyone pees in the pool.” Ryan Lochte has also made a similar admission. In fact, it’s been estimated that every competitive swimmer adds 25 to 117 milliliters of urine to the pool per event.

So if Olympians do it, should you use the pool as your potty, too? Not so fast, says Ernest R. Blatchley III, PhD, a professor of environmental and ecological engineering at Purdue University. In a 2014 study, published in Environmental Science & Technology, he and co-investigators found that uric acid — one of the primary chemicals in urine — reacts with chlorine to generate potentially hazardous chemicals. “Chlorine has the ability to kill microorganisms,” Blatchley tells Yahoo Health, “but it doesn’t ‘kill’ any chemicals — it has the ability to alter them.”

Related: Why Swimming Pools Turn Hair Green (It’s Not the Chlorine!)

One such uric acid-chlorine byproduct, cyanogen chloride, “has been used as a chemical warfare agent,” Blatchley says. Although this dangerous chemical usually breaks down quickly after it’s formed, thanks to the remaining chlorine in the pool, that may not happen if the chlorine has been severely depleted — for instance, if there’s a large crowd of swimmers, many of whom are peeing in the pool, causing the disinfectant level to drop.

Another worrisome chemical that forms when uric acid reacts with chlorine is trichloramine — which has been linked to a number of respiratory ailments, including asthma, says Blatchley. “You’re probably familiar with the odor around swimming pools. You may have identified that odor as being chlorine,” he says. “What you’re more likely smelling is trichloramine.”

As a volatile chemical, trichloramine easily transfers from the liquid phase to the gas phase, especially if lots of people are splashing in the water. The result? The air around the pool becomes contaminated — meaning swimmers are then inhaling a chemical with the potential to do respiratory damage.

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It’s not just urine that turns toxic when mixed with chlorine. Sweat contains many of the same organic compounds as urine, which means jumping into the pool without showering is also a no-no.

Bottom line: If you wouldn’t want to swim in somebody else’s urine, don’t make everybody else swim in yours. Blatchley compares it to the problem of secondhand smoke: “If you came across one person who smoked, you would probably have trouble quantifying the [health] effect. But if you encounter a lot of secondhand smoke, then the effect starts to become relevant.” So instead of assuming you’re the only mischievous swimmer, assume everyone is — and be the first one to hit the ladder and head to the toilet.

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