This Is What Happens If You Don't Clean Your Water Bottle

There’s no bond quite like the one you have with your emotional support water bottle. It’s faithfully by your side whether you’re at work, at the gym, or out on the town. It rides in tote bags and car cup holders, and it even rests by your bed as you sleep. Your water bottle is practically a best friend. But hey — when was the last time you washed it?

According to a poll by the team at resource site WaterFilterGuru, who surveyed over 1,000 TikTok users, 15% of respondents admitted they only clean their reusable water bottles a few times a month. That’s a lot of folks walking around with nasty Nalgenes and stinky Stanleys, yet most people aren’t aware of exactly what happens when you don’t wash your water bottle. Are you actually drinking viruses, bacteria, and fungi with every sip?

With the popularity of WaterTok, it’s good to know what’s going on inside your bottle, says Brian Campbell, the founder of WaterFilterGuru. This is especially pertinent since so many WaterTok recipes include fruits and sweeteners, which can make your reusable bottle more susceptible to bacteria buildup. This is true even if you sip regular H₂O, though, since bacteria are truly everywhere.

Ready for the cold hard facts? Keep reading to see what happens if you don’t wash your water bottle, according to a germ expert.

What’s Inside Your Dirty Water Bottle?

The average reusable water bottle lives a tough life. Not only are you constantly opening it and touching it to your mouth, but you might also be dumping in fruit, syrups, and ice, and potentially sharing sips with friends. With all that going on, it makes sense that they’re a breeding ground for all sorts of icky, sticky germs.

According to Jason Tetro, a microbiology expert and author of The Germ Code, you’re looking at bacteria, fungi — especially if you’re opening your water bottle in various different environments — and there’s also a potential for viruses, which is important to know if you’re sharing your water bottle with someone else.

As you use and reuse your water bottle without washing it, a sticky film will start to form on the inside, and that’s what collects germs — even if you give it a good rinse. Here’s how it works: First, you’ll get the type of bacteria that form something called a biofilm, Tetro tells Bustle, which is basically a sticky flytrap for germs. There are only a few species of bacteria that are known for creating a biofilm. And guess what? It just so happens that a few of them come from your mouth.

After you fill up your water bottle and drink from it, the germs from your mouth backwash into the bottle, which introduces the bacteria, says Tetro. Then, other bacteria can enter your bottle from the fruit, sugars, ice, or syrups you add. As you sip throughout the day and expose your bottle to the air in different environments, other nasties can find their way in and settle on the film.

Also, sorry to the straw stans, but Tetro says tumblers with built-in straws are more prone to collecting germs. “A straw is no doubt going to have a higher level of microbes as a result of the fact that you are putting a lot of focus on it with your mouth, and there’s going to be backwash as a result,” he says. “The mouth bacteria that you have is going to get into that straw and it’s going to go down as you remove the suction.”

On a positive note, it usually takes several days for a biofilm to form, so it isn’t like your water bottle instantly turns into a Petri dish. “If you were to take a water bottle, fill it up, drink from it, and then leave it there for seven days, you’d start to notice some slimy-ness in the water bottle itself,” Tetro says. “After a week is when you get those biofilms going.”

What Happens If You Drink From A Dirty Water Bottle?

For the most part, nothing bad will happen if you drink from your dirty Stanley Cup. “The number of bacteria in your water bottle will probably still be far less than the number of bacteria that are currently living in your mouth,” says Tetro. It’s why you’re able to drink from a mildly dirty water bottle and still feel OK. It’s your own mouth bacteria, after all.

“The real risk is the introduction of bacteria that you’re not used to or a fungi, because nobody wants to eat fungi unless it’s on cheese,” Tetro notes. “That’s really the reason to wash your bottle — to prevent the introduction of unknown microbial species into your body.”

It is important, however, to wash if you’ve shared your water bottle with a friend or if you’ve been sick. Certain bacteria, fungi, and viruses can impact your respiratory health, oral health, and gastrointestinal health, Tetro says, so it’s best to err on the side of caution and give that Hydroflask or Yeti tumbler a bath.

The Best Way To Clean Your Water Bottle

Unfortunately, a quick swish with tap water won’t remove bacteria, especially if that pesky biofilm has formed and trapped a selection of scum. Tetro recommends washing your bottle (and straw!) with the hottest water from your sink — or boiling water from a kettle — on a daily basis to kill the bacteria that lead to a biofilm so that it doesn’t form. “Once a week it’s always good to give it a nice wash-through with a bottle brush and a little bit of dish soap,” he says.

Tetro notes that stainless steel water bottles will be easiest to clean since they can handle boiling H2O, but a neoprene bottle can also take a hot water bath. If it says it’s microwave-safe, go ahead and give it a steamy rinse. As Tetro says, “The heat is going to kill the bugs.”

How Often Should You Clean Your Water Bottle?

The reality is that reusable water bottles should be rinsed daily, and ideally deep-cleaned once a week to prevent bacteria buildup. As Campbell says, “Bottles should be deep cleaned more often if you’ve been sick, if you drink while eating, or if you fill it up with something other than plain water.” (Looking at you, WaterTok.)

If you’re feeling lazy, put your bottle through a quick test to see if you can wait one more day before washing. Tetro says you can check for a biofilm by shining your phone’s flashlight inside and looking for grime. “You can also do a smell test,” Tetro says. If your water bottle smells funky, you should probably give it a wash.

Studies referenced:

Cugini, C. (2019). The role of Exopolysaccharides in oral biofilms. Journal of Dental Research, 98(7), 739–745. https://doi.org/10.1177/0022034519845001.

Experts:

Brian Campbell, founder of WaterFilterGuru

Jason Tetro, microbiology expert, author of The Germ Code