This Everyday Item in Your Gym Bag Could Be Hiding Millions of Germs, Study Finds

When you go to the gym, you're probably somewhat aware of how many germs are creeping around the place, from benches and free weights to machines and treadmills. But another item you use at the gym might actually be the dirtiest thing there, and it's not what you'd guess. Reusable water bottles, while important for staying hydrated and cutting down on single-use plastics, can quickly become a bacterial breeding ground surprisingly fast, according to a new experiment from WaterFilterGuru.

Over the course of a month, researchers tracked microbial growth in reusable water bottles using bacterial swab tests to see how fast germs can multiply. Each bottle was filled with distilled water, briefly sipped to simulate everyday use, and left untouched for one day, one week, and one month. At each stage, samples were cultured in a lab to count colony-forming units (CFUs), which measure visible bacterial colonies from a single cell.

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After just 24 hours, bottles had around 50 CFUs. One week later, that number jumped to 5.5 million CFUs, and by the end of the month, bacteria levels had surged past 30 million CFUs. To put it in perspective, after a week, a reusable water bottle contained more than 10,000 times the bacteria of a toilet seat and 22 times more than an airport check-in kiosk. Gram-negative bacteria, which are often associated with infections, dominated the growth, shedding light on the potential health risks of not regularly washing your water bottle.

How Often Should You Wash Your Water Bottle?

All this to say, washing your bottle daily and giving it a deep scrub every week keeps bacteria from multiplying. Reusable water bottles are one of the best trends for the environment, but neglecting washing them can turn a healthy habit into a germ-filled risk. No matter how clean it looks, your bottle could be hiding more germs than you could even imagine, and taking a few minutes to clean it is far easier than dealing with the potential health consequences of ignoring it.

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