Yuck! What’s Really in Your Swimming Pool?

Reviewed by Arefa Cassoobhoy, MD, MPH on July 01, 2015

July 1, 2015 -- That sparkling blue water looks cool and inviting on a scorching summer day. But do you really know what you’re getting when you dive in the pool?

Let’s try pee and poop for starters. And if you think chlorine totally protects you from that and other yucky stuff, think again.

“People believe that the water is sterile because it’s a pool with chlorine in it, but the reality is as soon as you stick a human body in water, it’s no longer sterile. There are bacteria and germs that can get in the water,” says Thomas Lachocki, PhD, CEO of the National Swimming Pool Foundation.

Those bacteria and germs, which come from you and your fellow swimmers, can make it harder for chlorine to do its job.

One major culprit: urine. The true reason swimmers get red, irritated eyes is not the chlorine itself, but from a reaction caused when pee mixes with chlorine, Lachocki says.

When chlorine is battling urine and other wastes, it loses the ability to fully protect us from other lingering pool germs, says Michele Hlavsa, RN, MPH, chief of the CDC’s Healthy Swimming Program.

“The chlorine is busy mixing with what we bring into the water, and there is less chlorine to kill the germs. We are kind of using up the chlorine with what’s washing off of our bodies,” Hlavsa says. Studies show the average person brings into the pool:

  • 0.14 grams of poop
  • One or two soda cans’ worth of sweat
  • One cup of pee
  • And billions of skin microbes

Children can carry as much as 10 grams of poop into the pool. “If 1,000 kids go to a waterpark, then 10,000 grams -- or 22 pounds -- of poop will potentially rinse off of their bodies into the water,” Hlavsa says.

Other Risks Afloat

Pool water can also carry diseases such as norovirus, E. coli, and legionella. Chlorine kills those, but in the small window of time before the germs die, swallowing even a small amount of water can make you sick.

But cryptosporidium, a type of parasite found in diarrhea, can survive in chlorinated water for up to 10 days and make you sick for weeks.

In a 2012 CDC study, researchers looked at 69 swimmers who were sick with waterborne illnesses. Out of those 69, over half were sick with the parasite crypto.

“Crypto is kind of resistant to the chlorine,” Lachocki says.

State or local governments set rules to keep public recreational pools and spas in check. But only 68% of local health departments regulate or inspect public swimming pools, according to the CDC.

The health department and CDC recommend that chlorine levels be between 1.0 to 3.0 parts per million (ppm).

What You Can Do

Lachocki suggests buying a testing kit to regularly check a pool’s chlorine and pH levels. Too many germs can cause chlorine levels to drop.

“It’s really up to the swimmers. It’s all about being proactive and protecting your health,” Hlavsa says.

They also suggest that you shower before swimming, and stay out of the pool if you're sick.

Other ways to avoid the spread of germs:

  • Avoid getting water in your mouth and swallowing it.
  • Don’t pee or poop in the water.
  • Regularly take bathroom breaks.
  • Check diapers every hour and change them away from poolside.

For more information on pool health and safety, Hlavsa recommends you look at the CDC’s healthy swimming site.

Show Sources


CBS News: “CDC finds public swimming pools rife with fecal contamination.”

Centers for Disease Control and Prevention: “Chemical Irritants (Chloramines) & Indoor Pool Air Quality.”

Centers for Disease Control and Prevention: “Cryptosporidium (‘Crypto’).”

Centers for Disease Control and Prevention: “Decoding the MAHC.” 

Centers for Disease Control and Prevention: “Healthy and Safe Swimming: Pool Chemical-Associated Health Events.”

Centers for Disease Control and Prevention: “Pool and Spa Test Strips Home Test Instructions.”

Centers for Disease Control and Prevention: “Recreational Water Illness (RWIs).”

Centers for Disease Control and Prevention: “The Three Es of Health Swimming.”

Centers for Disease Control and Prevention: “Tools and Forms for the Model Aquatic Health Code (MAHC).”

Centers for Disease Control and Prevention: “Your Disinfection Team: Chlorine & pH.”

CNN: “Yuck! What’s in your pool water?”

Hlavsa M. Morbidity and Mortality Weekly Report, published online June 26, 2015.

Men’s Health: “The Grossest Things in Your Swimming Pool.”

Michele Hlavsa, RN, MPH, chief of Health Swimming Program in the domestic water, sanitation, and hygiene team in the national center for emerging zoonotic and infectious diseases, CDC

Thomas Lachocki, PhD, CEO of National Swimming Pool Foundation.

Water Quality and Health: “Swimming Pools Myths Busted over the Airwaves.” 

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