And the (gross) reason your eyes turn red in the water.

By Liz Steelman
Updated July 02, 2015
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Ever emerge from the pool with some seriously red eyes? Turns out it’s not from chlorine. Pool-induced redeye is actually caused by chloramines, a byproduct of chlorine breaking down from urine, fecal matter and other contaminants. (Don’t worry if you didn’t know: According to a recent report from the CDC, the Water Quality and Health Council and the National Swimming Pool Foundation, more than 70 percent of people incorrectly believe chlorine causes red, irritated eyes). And that “chlorine smell”? Turns out, that’s actually chloramines too. A truly clean pool shouldn’t have a chemical smell at all.

The amount of contaminants in pools is truly alarming. In a March 2017 study published in Environmental Science & Technology Letters, researchers from the University of Alberta monitored for acesulfame potassium (ACE)—an artificial sweetener that the human body can’t break down and is detectable when urine is in water—in public pools for two weeks. They found that the concentration of ACE in pools was 570 times greater than in tap water, and they estimated pools contained anywhere between 7.92 and 20 gallons of urine.

The bad news is that when chlorine is busy working on all this urine and fecal matter, that means there’s less of it available to kill off chlorine intolerant germs such as E.coli or norovirus. So what’s a concerned swimmer to do? “Take control of the water you’re swimming in,” says Michele Hlavsa, chief of the Healthy Swim Program for the Centers for Disease Control & Prevention. Here are her five best tips to swim safely all summer long.

Check Inspection Scores

Much like the restaurants in your neighborhood, many local health departments inspect and score public pools, water playgrounds and parks. These public records are available online through your county or state department. For example, Florida offers a database searchable by location information like zip code or address, or test results that range from Satisfactory to Corrective Action to Stop Use. Check for yourself that the pool your family visits doesn’t violate any health codes. If your community doesn’t inspect or electronically post scores, Hlavsa recommends contacting your state and local health department, as well as elected representatives, to request they thoroughly inspect the establishment.

Test the Chlorine Level

Before your kids cannonball into the pool, make sure the chlorine level is appropriate to kill germs. A healthy pool should have little or no chemical smell. To really make sure, you can dip a four-way test strip in the water to get a reading of the water’s free-chlorine and pH in just 30 seconds. Compare the color of the strip to the key on the back of the packaging to decipher the reading. Hlavsa says the recommended level for pools should be 1.0 to 3.0 parts per million with a pH between 7.2 and 7.8. A manager might test every couple hours, but the levels can fluctuate depending on how many swimmers are in the pool and what contaminants are on their bodies. Sweat, urine, fecal matter and dirt can enter the pool when swimmers don’t shower before entering the water, or when someone defecates in the pool. And when contaminants fill the water, that means chlorine is less able to break down other germs.

To Buy: Aqua Chek Yellow Test Strips Free Chlorine, $8 for 50 strips,

Take a Break

Corral everyone out of the pool once an hour for a bathroom break and rinse off again before you head back to the pool. If your child isn’t potty trained, check the swim diaper once an hour and change as needed: they don’t keep pee and poop from leaking. “If water is getting in, water is getting out,” says Hlavsa. And if you or your child experience diarrhea, don’t go to the pool at all.

Know about Crypto

Cryptosporidium, a teeny-tiny bacterium that causes diarrhea, nausea, vomiting and stomach cramps has gained steam this past decade. According to Hlavsa, this microorganism caused the most waterborne disease outbreaks in the U.S. spread through fecal matter. And scarily enough, parasites can survive for more than 10 days in a pool with standard chlorination. It enters pools when someone swims with diarrhea. The most effective protection against crypto is not swallowing pool water or having it come in contact with the mouth. And to prevent others from becoming ill, stay out of the pool when you or your child is experiencing diarrhea (we can’t say it enough times).

Clean the Kiddie Pool

Waterborne illness doesn’t just lurk in the pool. Bacteria enter the kiddie pool you keep in the backyard, too. To keep your kids safe next time they splash around, you need to do more than just a quick rinse. “Dump the water, scrub it clean and leave it in the sun for four hours,” says Hlavsa. Crypto’s kryptonite? Ultraviolet rays from the sun.