I regularly rinse my gym water bottle with some water before refilling it again for another day, but I sometimes worry about how gross this habit is. When I asked experts about how long I can safely go without properly cleaning my water bottle, they were pragmatic but firm. You don't need to clean your water bottle with soap and water after every single use — but there's a tipping point when simply rinsing with water is no longer safe for your health.
Microbiologist Jason Tetro, known as "The Germ Guy," said three days is his recommended limit for rinsing his water bottle with just water. "After three days, you should be rinsing with soap and water," Tetro said. And "by the time you get to five days, you better be scrubbing that down."
It's not the water that's the problem, but your saliva, because that's "basically food for bacteria," said Chuck Gerba, a microbiologist at the University of Arizona.
"If your water bottle only has water in it, it's fine to refill it throughout the day without washing it," said Supriya Rao, a doctor. "Keep in mind though, bacteria from your mouth are introduced every time you take a sip. Those bacteria can multiply, especially if the environment is moist. This can lead to a buildup of biofilm, which you can't really see."
And if you're adding sugars or flavoring to your gym bottle, then you should "absolutely" be washing it with soap and water after you finish, because that increases bacteria, Rao added.
In general, try not to go longer than three days without cleaning your water bottle with soap and hot water. "We've sampled a few water bottles from students that walk around campus all the time with them, and in about three or four days, they get really contaminated," Gerba said. He said the water right out of the mouthpiece gets especially contaminated since it interacts with your saliva a lot.
"Generally, if you're the only one using it, the risks are fairly minimal, but once a week minimum, rinse it with soap and water," Gerba said. He recommended putting your bottle in the dishwasher so the hot water helps kill bacteria. This three-day maximum guideline applies only if you're not sharing your water bottle. Once you pass a bottle around, Tetro cautioned, you could pick up something your body isn't used to.
When in doubt about when to clean your bottle, follow your nose. If your bottle smells, bacteria waste has likely built up enough for your nose to notice. "The smell test is always the best option," Tetro said. "If you open it up and you smell and it's just funky, then don't drink out of it."
Many of us lead busy lives, which is why you should take it from the pros. Tetro, for example, will do a daily hot rinse of his water bottle in water that is "over or getting close to 160 degrees Fahrenheit," he said. "The reason I look for that temperature is because bacteria, viruses, fungi, they all die at 160 degrees Fahrenheit and above." See this hot water rinse as insurance to buy yourself a little more time between deep cleans.
But regardless of his hot water rinse, Tetro will still regularly clean his water bottle with soap. "Once a week or every five days, you want to use a little bit of soap and a bottle brush just to scrape in there," Tetro said.