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    15 Facts About Pool Water That Are Slightly Horrifying

    You'll never think about swimming pools the same way again.

    Pools are a glorious part of summer, but they aren't always as clean as they look.

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    Don’t worry, this isn’t a post for germaphobes about why pools are disgusting and why you should avoid them forever. We don't live in a sterile world, so it's totally normal for pools to have germs, like everything else. Besides, many bacteria are harmless and found naturally in the environment and on our skin. It's the pathogens you want to avoid: any bacteria, virus, or other organism that causes infection and disease.

    Most people (looking at you!) accidentally swallow some pool water while they're swimming.

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    Adults ingest on average half an ounce of water every time they swim, while kids usually swallow double that, germ expert Kelly Reynolds, PhD, at the University of Arizona, tells BuzzFeed Health. All that splashing, diving, and spitting can actually allow waterborne pathogens into your system, like ones shed from actual poop, which can obviously make you sick.

    So, here are 15 very good reasons you should try extra hard not to swallow any pool water this summer:

    1. Over 89 million people swim in public pools each summer, which makes it a popular place to swap germs.

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    Honestly, most public pools will probably test positive for a disease-causing pathogen, according to Reynolds. Even if the pool is maintained and properly chlorinated, you're dealing with A LOT of people in a SMALL amount of water, creating basically a breeding ground.

    "Because so many people go into pools, there's a huge exposure potential if there happens to be disease-causing bacteria or pathogens — so a single pool can cause a mass outbreak," says Reynolds.

    2. Everything — sweat, dirt, oil, grime, bodily fluids — on a person eventually ends up in the water.

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    Granted, most of the nonpathogenic things that come off of your body are just really gross and won't make you sick simply by swimming in them. But if you wouldn't drink someone else's bath water, you might want to think twice about opening your mouth in a pool.

    Plus, a surprising number of people can carry pathogens on their body without it harming them. For example, about half of the population carries Staphylococcus aureus. So you never really know what you're swimming in.

    3. Chlorine does kill germs, but it can't always outweigh the sheer number of people in and out of a pool.

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    You know when the chlorine is so extra that you can still smell it on your skin afterwards? That's actually a good thing, says Reynolds. Maintaining proper chlorine levels is crucial because the chemical does a great job of killing off staph and other bad bacteria. But those chlorine levels should be checked every two hours to make sure they're still high enough, and that doesn't always happen.

    "It's difficult to maintain the proper chlorine concentration in a small volume water and large quantity of people shedding germs and feces," Reynolds says. So it's often depleted and slightly ineffective.

    4. Chlorine is also depleted by things like sweat, sunscreen, and skin or hair products.

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    "All the things we put on our body like lotion, shampoo, conditioner, sunscreen, etc., remove or absorb the chlorine from the water, so there's a lower concentration than there needs to be to kill all the germs," Reynolds says. That's why it's hard to keep a pool actually germ-free throughout the whole day.

    5. There's legit so much poop in the water.

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    "In a typical busy public pool or water park, there are several pounds of feces shed in the water by the end of the day," Reynolds says. DISGUSTING.

    That's because we all have a little residual feces on our bodies unless we're literally soaping up or using a bidet throughout the day, says Reynolds. Adults shed an average of 0.14 grams of feces, which is equivalent to the weight of one pea, and kids can carry up to 100 times that amount — so 10 peas' worth of fecal matter!

    6. Poop can carry nasty pathogens like hepatitis A and E. coli.

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    Fecal matter will carry any disease spread through the fecal-oral route, including bacteria like E. coli, shigella, campylobacter (food poisoning), and vibrio. It can also carry viruses such as hepatitis A and typhoid, and parasites like giardia and cryptosporidium.

    Even if you don't feel sick, these germs can still be found in your poop. Some people even carry strains of E. coli that don't make them sick but can seriously infect others.

    "If we thought about our drinking water having any fecal organisms in it, we'd panic and stick to bottled water — but we don't think twice about putting our head under in a pool contaminated with the same bacteria from poop," Reynolds says.

    7. Urine won't really harm you, but it makes the chlorine less effective at killing other germs.

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    "Contrary to popular belief, urine is not sterile — but the type of bacteria in urine which causes infections like UTIs is actually killed very easily by chlorine," Reynolds says.

    However, this comes with a catch: Too much urine will deplete the chlorine concentration in the pool water so it's less effective at killing the bad germs like E. coli or shigella. "Not peeing [in the pool] is really for your own good and the health of other people," Reynolds says.

    8. Most people in the US don't shower before they swim.

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    It might seem counterintuitive to shower before jumping in the water, but otherwise the pool basically becomes a giant bathtub of dirty bodies.

    "Showering both removes the bacteria and fecal matter from your body and it also rinses off all the sweat and products which will deplete the chlorine," Reynolds says.

    Apparently Americans are particularly bad at this, while showering before you swim is pretty common practice in Europe. "This may be more of a cultural thing, even though it's primarily for our health and safety," says Reynolds.

    9. Research has shown time after time that swim diapers leak.

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    There's a reason why baby pools exist — and it's not just for safety. "The fact is that swim or water diapers just don’t work — we've done countless studies using sand and food coloring and we know it seeps out no matter what," Reynolds says.

    Obviously babies and toddlers should be able to swim with their parents, but if they're in a swim diaper, it's probably best for everyone if they're in the baby pool, says Reynolds.

    10. Someone who had diarrhea within the past two weeks can still shed diarrhea-causing pathogens into the pool.

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    Yes, two weeks sounds like forever, but the CDC warns that this is the amount of time during which the body can shed diarrhea-causing pathogens. "Even if you feel better and you don't have symptoms, you can still be shedding millions, even billions, of diarrhea germs into the pool," Reynolds says.

    Given that 89 million people are swimming in pools each summer, that's a lot of people who either have diarrhea or are recovering from it and still shedding their germs. Unfortunately, not many people know about this rule, or how risky it is to leak some diarrhea in a pool, so just don't open your mouth underwater. Ever.

    11. Accidental poops from kids, not just babies, are way more common than you think.

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    We all know that little kids pee in the pool, but Reynolds says they also poop (even if it's just a tiny bit) in the water way more often than you'd like to think. Like, all the time.

    "If the stool is hard and solid, you have a few minutes to get it out of the water before it dissipates, but if it's loose — it'll spread immediately," Reynolds says. And obviously kids don't always tell an adult that they pooped — so hours could go by before someone notices.

    12. Cryptosporidium, the number one cause of pool outbreaks, is actually chlorine-tolerant.

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    Cryptosporidium is a parasite that causes severe diarrheal illness lasting for weeks; and there's no cure or antibiotic, so you just have to wait it out. "Crypto is easily passed through feces and it causes most recreational water illness outbreaks, and even a few deaths, each year," Reynolds says.

    Crypto is so much worse than the other germs because it's chlorine-tolerant and can survive for days in the water. It's also shed from your body for a long time after you get sick, even when you feel better, says Reynolds. So the people who bring it into the pool probably aren't even aware — and it takes only a little bit of contaminated feces to contaminate an entire pool with crypto.

    13. It takes just a tiny bit of pool water to make you sick.

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    Think about how you avoid using tap water, even for brushing your teeth, in countries without water sanitation. You should adopt the same mindset and take similar precautions with pool water, says Reynolds. It only takes a little bit splashed in your mouth to get in your system.

    14. Chlorine shocks can kill all the germs, but they don't happen very often because the pool has to be shut down.

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    Hyperchlorination is a practice used to "shock" the water and kill all of the germs and pathogens, including cryptosporidium. "It's effective, but you have to shut the pool down for at least an entire day," says Reynolds. So it's a huge inconvenience and operating cost for the pool, which is why chlorine shocks don't happen all the time.

    15. The rate of illness outbreaks from swimming pools is growing.

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    As pools become more popular and accessible to the public, this also creates more opportunities for outbreaks. "We've reached an all-time high in recreational water outbreaks from cryptosporidium and other pathogens," says Reynolds. For example, Reynolds says that there were 78 documented outbreaks in the last year in 31 states, and 74% of those pools passed as properly chlorinated.

    Fortunately, "the CDC is working on a model aquatic health code which suggests federal guidelines for public pools," Reynolds says.

    So enjoy the pool this summer, but just try not to open your mouth.


    Adults shed an average of 0.14 grams of feces, which is equivalent to the weight of one pea, and kids can carry up to 100 times that amount — so 10 peas' worth of fecal matter. An earlier version of this story misstated these measurements.