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June 30, 2017 -- The holiday weekend is upon us, which for many Americans means it’s time to fire up the grill, plan a picnic, and head to the pool.

But while swimming pools and water parks look refreshing, dangers can lurk in them.

Indiana health officials shut down a water park in June after two children got chemical burns from chlorine in the water -- reportedly a result of an equipment malfunction.

But a more common danger comes from something else: urine. And it’s staggering how many people are peeing in pools.

So how can you keep yourself and your family safe while swimming? WebMD takes a closer look.

Peeing in the Pool

It’s a hard truth, but after 20 years studying swimming pool chemistry, Ernest Blatchley III, an environmental engineer at Purdue University, is willing to tell it like it is: People pee in swimming pools.

“It’s fair to assume that any pool that has people in it, also has urine in it,” Blatchley says. “What we have found is the average swimmer leaves about roughly the equivalent of a shot glass (1 to 2 ounces) of urine in the pool.”

Blatchley says he’s never studied a pool that didn’t have urine in it.

“If one person pees in a pool, it probably doesn’t make a difference. But it’s not a situation where only one person is peeing in pools. There is a large fraction of people who regularly pee in pools,” he says.

That’s what researchers at the University of Alberta recently found, too. In a study published in March, researchers collected samples of the artificial sweetener acesulfame potassium (ACE) from 31 different swimming pools and hot tubs and found high levels of the sweetener in every location.

Based on the amount of sweetener, researchers estimated that a 220,000-gallon pool would have an average of 20 gallons of urine.

“This provides us evidence that people are indeed urinating in pools,” says researcher Lindsay Blackstock, who was involved in the study. The only way it gets into swimming pools or hot tubs is from urine, she says.

Blackstock says urine in recreational water isn't necessarily a risk for swimmers. But things like urine and sweat can react with chlorine to create toxic compounds known disinfection by-products, or DPBs, she says.

The potential health issues include more asthma in elite swimmers and less-major respiratory and skin issues sometimes seen in swimmers, lifeguards, and pool workers.

Susan Richardson, PhD, an environmental chemist at the University of South Carolina in Columbia, says there is definitely a risk for asthma from these compounds, mostly among Olympic athletes and other swimmers that spend a lot of time in pools. A recent university study found more than 100 chemicals in pools and hot tubs, some of which are toxic.

"Like anything, it depends on the dose and contact time. So, how many hours per day and how many days per week you would spend in a pool," Richardson says. "I think the risks are much lower for the casual swimmer."

Still, scientists say it is important to know that when your eyes get red in the pool or you smell that classic "chlorine" odor, it’s not due to chlorine.

“A healthy pool doesn’t have a chemical smell,” says Michele Hlavsa, RN, chief of the CDC’s Healthy Swimming Program. “It’s not the chlorine that is making your eyes red, it is the urine and sweat that combines with the chlorine,” she adds.

It also cuts the amount of chlorine that's left to kill germs, she says.

Scientists are looking for solutions. Richardson says her team is looking into a promising new treatment that uses silver/copper disinfection and doesn't rely on much chlorine, or potentially no chlorine at all. They are testing it in pools in Myrtle Beach, SC.

"From what we can tell so far, it does a great job keeping the water clear and disinfected, without necessarily needing to add chlorine," Richardson says.

Health Outbreaks

Fecal matter (poop) can find its way into water by washing off people’s bodies when they swim. This can be a more serious health risk, since fecal matter has germs like cryptosporidium that can cause gastrointestinal illness.

Pool management is important on this front, and not all local and state governments inspect swimming pools. You can go online to see if yours does and check to see if it has been cited or closed for any violations. Results might also be posted at your pool or water playground.

The CDC says that when state and local health departments inspected almost 50,000 public pools in 2013, 12% of inspections resulted in immediate closures of pools for serious public health violations, often because there was no disinfectant in water or no safety equipment.

Hlavsa, the CDC’s pool safety researcher, says it is important to know that while chlorine kills most germs within minutes, it doesn’t kill them instantly. “When we swim and are ill with diarrhea, we are potentially sharing germs. We share water. We immerse bodies in it, and sometimes we swallow it,” she says.

A May 2017 CDC report showed that cryptosporidium outbreaks linked to swimming pools and water playgrounds doubled from 16 to 32 between 2014 and 2016. The federal agency says it’s not clear if outbreaks are on the rise or outbreak detection is improving. Hlavsa says the good news is overall, those numbers are small. “We are swimming hundreds of millions of times a year. Most of us, most of the time, will be OK,” she says.

Still, she says the CDC warns that “swallowing just a mouthful of water contaminated with crypto can make otherwise healthy people sick for up to three weeks with watery diarrhea, stomach cramps, nausea, or vomiting, and can lead to dehydration."

Despite the dangers, Hlavsa doesn’t think any of this should scare people away from pools. They can be fun and are a great place for exercise and outdoor activity. In fact, she says she swims often with her two young children.

“When we bike, we put on helmets. When we drive, we put on seat belts. This is the same thing. We are sharing water,” she says. “So it’s not about avoiding swimming. It’s about being healthier and smarter about the way we are swimming.”

Other summer safety tips:

  • Do your part to keep the pool clean. Practice good hygiene. Before getting into the water, use the bathroom and at least rinse off in the shower to remove any sweat, urine, poop, or excess personal care products.
  • Don’t urinate in the pool, and teach your children the importance of not doing that, too.
  • Help maintain water quality. If you or your child is sick with diarrhea, don’t swim. Don’t swallow water in the pool. People with weakened immune systems should also talk with their health care provider before swimming.
  • Take kids on bathroom breaks every hour while at the pool, and check your children’s diapers regularly.
  • Don’t sit on splash park or playground water jets.
  • Use test strips to check the pH and chlorine concentrations of your pool. They are widely available online and at big-box stores, cost around $10 for a bottle containing many of them, and they are easy to use. Generally, you stick a piece of the strip in the water for a few seconds and compare the colors the stick turns with a chart on the back of the bottle.
  • Designate a “water watcher” when you are with children who are swimming, even if there are lifeguards in the pool.
  • Also check the drain at the bottom of the pool. You want to see them secured and in good repair, and you want water to be clear so if someone is in distress near them at the bottom of the pool, you can see them.

To learn more about keeping your family safe in the pool this summer, visit

Show Sources

Ernest Blatchley III, Purdue University, West Lafayette, IN.

Michele Hlavsa, RN, CDC, Atlanta.

Susan Richardson, PhD, University of South Carolina, Columbia.

EJ Daiber, Environmental Science & Technology, April 28, 2016.

LK Blackstock, Environmental Science & Technology Letters, March 1, 2017.

M. Lomax, Open Access Journal of Sports Medicine, May 12, 2016.

CM Villanueva, American Journal of Epidemiology, January 15, 2007.

CDC: “Check out healthy and safe swimming,” “Make a health splash,” “Crypto outbreaks linked to swimming have doubled since 2014.” “Water Safety.”

Morbidity and Mortality Weekly Report: “Immediate Closures and Violations Identified During Routine Inspections of Public Aquatic Facilities.”

Morbidity and Mortality Weekly Report, May 20, 2016.

Morbidity and Mortality Weekly Report, May 19, 2017.

E.Yue, Elsevier, September 12, 2016.

J.H.Jacobs, European Respiratory Journal, 2007.

J. Westerlund, Annals of Occupational Hygiene, July 7, 2015.

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