(POPULAR SCIENCE) — Let’s start with the gross stuff: up to ten grams of poop can wash off a little kid’s butt in a pool. Ten grams is a pretty small amount, but now multiply that by the number of children in your average public pool. Think about how much poop that is. And now think about the last time you got an infection from swimming in a pool.

Was it last summer? The summer before that? To be fair, young kids are far more likely to get sick because they end up swallowing the water, so think back to when you were little. Anything? Probably not. Even if you spent most of your childhood in public pools, odds are you never got seriously ill from the bacteria and parasites in there.

To be clear: it’s not because pools are clean. Pools are awful. They’re full of poop and pee and probably some blood to round it all out, and lots of them don’t have the proper amount of disinfecting agents. 17 percent of people say they’ve peed in a public pool before (and let’s be honest, if 17 percent are willing to admit it, there have to be way more people who aren’t).

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