How Much Pee Is in Your Pool?

Michael Phelps, Ryan Lochte, swimming pool, pee
Olympians Michael Phelps (R) and Ryan Lochte (R) (shown at the 200m Individual Medley event at the Rio Olympics) are two of the many elite swimmers who say they pee in the pool — just like you and me. ODD ANDERSEN/AFP/Getty Image/American Chemical Society/YouTube

Michael Phelps' Olympics performance might have inspired folks to keep swimming just a little bit longer this year – but, please, get out of the pool to pee. Peeing in the water has long been the dirty little secret of swimmers, but, it's not just gross. An episode of the American Chemical Society's Reactions series tells us it's also bad for our health.

Scientists have known for some time that there are about 30 to 80 mL of urine per person in public pools. That's about a shot glass full for each (yum?). To counteract the urine – and other icky things floating in the water, like skin cells, sweat, dirt and used suntan lotion – people add chemical disinfectants to keep pools clear and "clean," and to keep us from getting some nasty ailments like Giardia and E. coli.


But are those disinfectants doing their job?

As it turns out, maybe not as well as you'd like. According to researchers, these disinfectants can react with urine, sweat and other organic matter to form disinfectant byproducts (DBPs) that can cause serious health concerns, especially for professional swimmers and people who work around pools.

DBPs can cause respiratory problems, such as asthma, and are the main reason for the red, burning eyes you may experience in the pool. And the No. 1 culprit is — you guessed it — urine, which causes half of the DBPs in the pool.

Urine contains urea, a chemical that reacts with chlorine to form trichloramine, the compound that makes a pool smell like a pool. (You'll never enjoy that smell again, will you?) It's also the one to blame for respiratory issues — a real problem for competitive swimmers who spend so much time in the water — and red, burning eyes.

But cutting down on DBPs is tough, since urinating in the pool is something almost everyone does — it's just easier than getting out to take a leak — and people mistakenly think the chlorine will kill any germs. Olympic swimmers like Phelps and Ryan Lochte even joke about their pool-peeing.

"High-profile swimmers have a real opportunity to take a position of leadership and responsibility," said Ernest Blatchley, an environmental engineer at Purdue University, in an article in Chemical and Engineering News. "The best thing that swimmers could do to improve the swimming environment for themselves and for everybody else who uses the pool ... is to practice commonsense hygiene."

That means first taking a shower before getting into the pool to rinse off much of the dirt, sweat and lotion our bodies carry around. And second, but most important: don't pee in the pool.