How Gross is It to Never Wash My Water Bottle?

This article originally appeared on Tonic. 

Ah, friends. They're like family but cooler. Fully customizable. Fall and one of them will be right there to pick you back up. But as great as friends can be, they also do a lot of really stupid stuff. Stuff that blows your mind. Like, sometimes it seems crazy that you even hang out with people who make such crappy decisions. Stuff that, were it to get out, would be mortifying for anyone with even a shred of self-respect. Lucky for your friends, they've got you to ask their deepest, darkest questions for them. And lucky for you, we started this column to answer those most embarrassing of queries.

The Scenario: A few years ago, your friend looked at the floor of her car and saw a disgusting collection of disposable water bottles staring back at her. To minimize her shame and become environmentally friendly, she gave up her Evian addiction and invested in a reusable water canteen. All seemed well.

She carried that plastic container around like a security blanket, until one day she dropped in on the ground outside of her car, and yelled, "Oh my god! Now I have to wash it!" This level of anguish struck you as odd because, shouldn't she be washing her canteen every night? When pressed on the subject, your friend admitted that she doesn't wash her water bottle regularly because she only uses it for water. "Water is already super clean," she said. Now you're worried your friend is going to get one of those Grey's Anatomy diseases that swiftly and mysteriously warrants brain surgery.

The Issue: "The world literally teems with bacteria, and there is a sort of artificiality in believing that drinking water is completely sterile," says Amesh Adalja, infectious disease physician and senior associate at Johns Hopkins Center for Health Security. A 2005 study indicates there are seven different types of bacteria found in bottled water three weeks after bottling— before the bottle touches human lips. While many of us have heard that we shouldn't reuse disposable water bottles because the plastic can harbor harmful bacteria, my friend assumes that reusable water bottles are magically immune to bacteria and germs.

The Worst That Could Happen: Oh, you know, nasty infections. A website best known for reviewing treadmills decided to commission an independent study to explore the types of germs living in our reuseable water bottles. While the study was not peer-reviewed or published in a journal, it might be worth acknowledging that it found that the average water bottle contains 300,000 colony-forming units of bacteria. While not all of them were bad, more than 60 percent of the bacteria they found fell under the harmful categories that cause illnesses like E. coli and strep. In surgical settings, these bacteria cause pneumonia, wound infections, skin infections, and even meningitis.

What Will Probably Happen: "I am unaware of anyone ever getting sick from [reusable] water bottles," says Kevin Urdahl, professor of immunology and researcher at the Center for Infectious Disease Research. "The amount of bacteria in the water bottles is undoubtedly tiny compared to the bacteria that already lives in our digestive tract." Adalja echoes this sentiment: "There is fecal bacteria in all sorts of water, and it is only when they reach high levels that it is a concern." Adalja does say though, that in cases of high bacterial levels, there is a minor risk of diarrheal illness.

In a study from the University of Calgary, researchers looked at the personal water bottles of elementary school students and determined that, given the poor hygiene of students' own hands, personal water bottles weren't recommended for young students. The amount of contaminants, like fecal matter, were just too high. Though a strong side-eye is in order here, hospitals are not overrun with people getting sick from their gross water bottles.

What You Should You Tell Your Friend: You should very politely tell your friend that she's disgusting, but probably not on death's door. If she wants to avoid the small possibility of diarrheal illness she should probably wash her water bottle with soap and water every day.

Additionally, you can mention that not all water bottles are created equal. Stainless steel containers are more resistant to bacteria and they don't crack and scratch the way plastic does—germs can nest in those cracks. Whether you're drinking purified water or a protein smoothie, Adalja suggests always dumping the contents that you don't consume and washing your canteen after each use. "All beverages have some degree of bacteria in them," he explains. "And there really is no major appreciable difference in these substances as it relates to cleaning your container."