Here’s a good reason never to swallow water from a swimming pool: A new study found telltale signs of feces in more than half of pools sampled in Atlanta last summer.

The problem is not confined to Atlanta, says Michele Hlavsa, a researcher who promotes healthy swimming at the federal Centers for Disease Control and Prevention: “I think if we had done this study anywhere in the United States, we would have found the same thing.”

And it’s not the fault of pool operators, Hlavsa says: “This is really about swimmer hygiene.”

In other words: There’s poop in our pools because people are not taking showers before swimming or are having accidents in the water. And public health officials care because sometimes that contaminated water makes people very sick.

For the study, published in the CDC’s Morbidity and Mortality Weekly Report, Hlavsa and colleagues tested water from filters at 161 pools, including 37 municipal pools, 89 club or membership facilities and 35 small water parks (which included any facility with so much as a spray feature, Hlavsa says). They found DNA from E. coli bacteria, normally found in the human gut and feces, in 58 percent of samples. That’s a “fecal indicator,” or proof that poop has rinsed off someone’s bottom or been deposited directly into the water, the report says. The tests did not indicate whether the bacteria were alive or dead. Municipal pools were more likely than other pools to show signs of fecal contamination.

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