Whether it’s the near infamous Stanley cups or the Naglene, covered in national park stickers, you likely have spotted reusable water bottles almost everywhere you’ve go. College campuses, cafes, the office, and of course, the gym or on a hiking trail. 

People carry reusable water bottles for a variety of reasons. Perhaps they want to reduce plastic waste or microplastic intake, or maybe they are trying to stay hydrated for health reasons. Regardless of the different reasons, there is one thing that reusable water bottle owners likely all do, and that is not wash their water bottles often enough. 

Studies have found that reusable water bottles carry a plethora of bacteria that could greatly impact your health. So, how often should you wash your water bottle?

Are Bacteria Hiding in Reusable Water Bottles? 

After discovering biofilm in his water bottle, Carl Behnke, an associate professor at Purdue University, specializing in food safety, and colleagues conducted a study on reusable water bottles around campus. 

The study team analyzed the water bottles based on age, material, if they used a filter, and what sort of beverages the owners put in them (usually water, coffee, tea, and soda). The results of the 2017 study were as one might fear: Reusable water bottles were hotbeds for bacteria. Most of the bottles in this study had high to unsafe levels of bacteria in them. 

The team noted that filtered and non-filtered bottles had a similar amount of bacterial growth and that bottles used for beverages other than water had higher bacterial counts. They also found that material mattered when it came to a cleaner water bottle. 

“As this study showed, among the four bottle materials examined (hard plastic, soft plastic, metal, and glass), glass bottles have the lowest reading of organic residue on the exterior surface. This might be attributed to the fact that glass is nonporous and easy to clean. Still, perhaps more importantly, it is easy to see when it is sufficiently clean, compared to plastic or metal bottles,” the authors wrote in the study.

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Water Bottles Need to be Properly Cleaned 

Of the Purdue study participants, nearly 85 percent claimed to wash their water bottles regularly, whether it be just a quick rinse or with soap and water. Of those who did wash their bottles, they only did so about once a month. However, a researcher from the University of Alabama at Birmingham notes that water bottles need to be washed more frequently and dried properly. 

“Mold spores, which are ubiquitous in the environment, can settle on damp surfaces and begin to grow,” Benjamin Turner, an instructor at the University of Alabama’s Department of Biology, said in a statement. “Additionally, if the water inside the bottle is not replaced regularly, organic matter from saliva or other contaminants can provide nutrients for mold to thrive.”

How to Clean Your Reusable Water Bottle

When it comes to cleaning your reusable water bottle, it’s something you may want to add to your daily routine. For best and cleanest results, follow the steps below: 

• Use hot, soapy water to scrub the interior and exterior of the water bottle. Including any straws or mouthpieces you may use. 

• Make sure to get all the hard-to-reach places where bacteria may grow, like in the lid. 

• Rinse thoroughly. 

• Once rinsed, you could use a food-safe sanitizing spray, like those used in restaurants, to kill any lingering bacteria. 

• Lastly, let the bottle air dry completely before putting it away or filling it up again. 

Other tools, such as a bottle brush, can come in handy when sanitizing your water bottle or running it through the dishwasher if it is dishwasher safe. Another way to mitigate bacteria growth is to only keep water in your bottle instead of tea, coffee, or other beverages.

This article is not offering medical advice and should be used for informational purposes only.

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Article Sources

Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:

A graduate of UW-Whitewater, Monica Cull wrote for several organizations, including one that focused on bees and the natural world, before coming to Discover Magazine. Her current work also appears on her travel blog and Common State Magazine. Her love of science came from watching PBS shows as a kid with her mom and spending too much time binging Doctor Who.