Look, at this point, we know that pretty much everything gets covered in fecal matter. Your iPhone. Your toothbrush. Your shoes. The water that we swim in and the roads upon which we drive.

Truly, the world is awash in that which comes from within us.

So it's not shocking that reusable water bottles, left unwashed, can become a breeding ground for bacteria and a safe haven for poop particles. Whether plastic or metal, screw top or squeeze, bottles that go days between cleanings can leave us gulping down germs with every drink.

An analysis last year from New Jersey-based EmLab P&K, an environmental testing firm, found water bottles carrying an average of more than 300,000 colony-forming units of bacteria per square centimeter.

That's roughly six times the amount of such bacteria found on pet bowls, the study said, and just slightly fewer than on the toothbrush holder sitting unwashed near your toilet.

For the study, conducted for the site TreadmillReviews.net, researchers swabbed a dozen water bottles used by athletes that hadn't been cleaned in a week. They used different types of bottles, too: Three squeeze top, three slide top, three screw top and three straw top.

To be clear, the EmLab P&K study isn't peer reviewed, but its findings are bolstered by comments from Charles Gerba, the renowned University of Arizona professor known as "Dr. Germ."

"Your hands may pick up viruses from touching various surfaces, which then get transferred to the bottle and eventually to your mouth," Gerba, a professor of microbiology and environmental sciences, told Shape.

Your mouth contains bacteria that can get into your bottle via backwash, but as Gerba told Self, your own germs that were already in your mouth won't harm you. New germs can, though. Those can come from sharing a bottle with another person, or from touching something gross — say, an iPhone with fecal matter on it — and then opening your bottle.

Slide-top bottles in the study were by far the grossest, carrying some 933,000 colony forming units per square centimeter. Straw-bottles, however, carried a mere 25.4 units per square centimeter.

Stainless steel bottles are naturally anti-bacterial and don't develop germ-harboring cracks, Shape reported, making them perhaps your best bet for a clean(ish) bottle.



To clean them, here's what the SIGG brand recommends: Hand-wash your bottle by filling it halfway with hot water and adding a teaspoon of unscented dish soap. After a few minutes, rinse the soapy water completely using warm water.

Follow Josh Hafner on Twitter: @joshhafner

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