Your reusable water bottle is probably disgusting. Here's what experts want you to know.

A woman is drinking out of a reusable water bottle.
How often should you wash your reusable water bottles? Here's what experts suggest. (Getty Creative)

These days, reusable water bottles are a popular accessory. Avoiding single-use plastic water bottles, which can contain thousands of tiny plastic pieces, and staying hydrated all day? It sounds like a win-win. Of course, there is a downside, and that downside is the potential germs your favorite Stanley tumbler or Hydro Flask may be harboring if you don't clean it thoroughly and often — which many people don’t.

You may think, hey, it’s just water in my bottle — what’s so dirty about it? Well, according to Dr. Alexander Mortensen, family medicine physician at the Mayo Clinic Health System, bacteria and mold require very little to grow, and your moist water bottle is the perfect environment for them to thrive. “The same way that reusing a water glass on your bedside table may not get you sick, the risk that any significant bacterial exposure has developed is low,” he says. “However, it is not zero, especially if the water bottle is not cleaned for some time, as bacteria and other pathogens can build up.”

Can you get sick from a reusable water bottle?

Microbiologist Jason Tetro, author of The Germ Code, tells Yahoo Life that we typically can’t get sick from stuff that’s already in our bodies — so, if you have the flu, you’re not going to keep giving yourself the flu when you use your reusable water bottle. Yet there are other ways your water bottle may be making you sick.

Reusable water bottles tend to go where we do, such as to the gym or office. When we refill our water bottle at a shared tap at the gym, for example, we may expose our bottle to bacteria or viruses from someone else’s mouth. (Gross, I know.)

Bacteria can form a biofilm, which is what happens when bacteria attaches itself to a “special kind of sugar” and starts to form a colony with other bacteria, leading to that slimy layer you might see in your water bottle when it hasn’t been cleaned recently. Ingesting the bacteria can lead to developing gastrointestinal problems or respiratory issues.

One way to avoid getting sick from your water bottle is to only refill it at home instead of at a public tap or water fountain, suggests Tetro. The water fountain at the gym in particular has been found to be full of bacteria, according to one study.

What about mold?

Mold is a category of fungus that loves damp places with limited airflow — like your water bottle. If you don’t wash your water bottle, mold can build up over time, which can in turn lead to health problems. The Centers for Disease Control and Prevention says that mold exposure can cause a stuffy nose, sore throat, coughing or wheezing, burning eyes or skin rash and can have a bigger impact on those with asthma or people who are allergic to mold.

Recently, a young woman in Georgia went viral after she claimed on TikTok that she ended up in the hospital with bronchitis from unknowingly drinking from a moldy water bottle. However, according to Dr. Shashank Ravi, clinical assistant professor of emergency medicine at Stanford Medicine, this is a very rare outcome, as “the most common form of bronchitis from mold is from inhalation, which requires large amounts of mold in the water bottle,” he tells Yahoo Life. It’s much more common, he notes, to see bronchitis from mold in humidifiers when they are not maintained and cleaned properly — but that’s a problem for a different day.

“While our immune systems do a great job of fighting many types of bacteria and fungi, for those who may have weakened immune systems or are ingesting large quantities of the bacteria or mold, that can make an individual sick,” says Ravi. “Think of it as drinking water from a stagnant pool of water. Risks can vary, from diarrhea and an upset stomach to certain organisms making their way to the bloodstream and spreading to other parts of the body."

How often do you need to wash your water bottle?

Prepare to give your water bottle a little extra TLC in order to stay healthy. “Water bottles are just like any other container that we use for our food or beverages and can harbor bacteria both from water sources or, more likely, our own mouths,” says Mortenson. “Bacteria and mold require very little to grow, and they have everything they might need in a water bottle.”

So how should you clean your water bottle? Both Mortenson and Tetro recommend washing your bottle with hot water and soap — ideally every day to prevent the growth of bacteria, says Mortenson. It’s also important to get in all the crevices, which is why it's worth investing in a bottle brush cleaner that’s able to get inside the parts of the bottle and scrub. If there’s a funky odor in your water bottle, avoid using bleach. Instead, soak it in baking soda or vinegar, which are safe for human consumption.

The important thing is that you don’t let your reusable water bottle sit for too long without a proper cleaning, as tempting as it might be to put it off. If you need motivation, imagine how you'd feel finding slimy biofilm inside your bottle — or mold around the lid. Save your water bottle from that fate and head for the sink instead.