Pools are a glorious part of summer, but they aren't always as clean as they look.
Most people (looking at you!) accidentally swallow some pool water while they're swimming.
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.
2. Everything — sweat, dirt, oil, grime, bodily fluids — on a person eventually ends up in the water.
3. Chlorine does kill germs, but it can't always outweigh the sheer number of people in and out of a pool.
4. Chlorine is also depleted by things like sweat, sunscreen, and skin or hair products.
5. There's legit so much poop in the water.
6. Poop can carry nasty pathogens like hepatitis A and E. coli.
7. Urine won't really harm you, but it makes the chlorine less effective at killing other germs.
8. Most people in the US don't shower before they swim.
9. Research has shown time after time that swim diapers leak.
10. Someone who had diarrhea within the past two weeks can still shed diarrhea-causing pathogens into the pool.
11. Accidental poops from kids, not just babies, are way more common than you think.
12. Cryptosporidium, the number one cause of pool outbreaks, is actually chlorine-tolerant.
13. It takes just a tiny bit of pool water to make you sick.
14. Chlorine shocks can kill all the germs, but they don't happen very often because the pool has to be shut down.
15. The rate of illness outbreaks from swimming pools is growing.
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.