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What Happens If You Drink Out of the Same Water Glass for a Week, According to Doctors

This seemingly harmless habit could put your health at risk.

Do you keep a glass of water next to your bed, refilling it each night without washing it? Or maybe you have a favorite water glass and use that same one for days on end, never bothering to put it in the dishwasher. After all, it's just water—is it really necessary to wash it?

According to doctors, yes. In fact, not doing so could result in a nasty illness, they say. "Norovirus, which is a highly contagious virus that causes vomiting and diarrhea, can survive for a week or more in an unwashed glass without adequate cleaning," Dung Trinh, MD, founder of the Healthy Brain Clinic, tells Best Life. Read on to find out what else he, and other doctors, have to say about the hygienic concerns around using the same water glass for a week (and then go load up your dishwasher!).

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Staying well-hydrated is crucial to our health.

woman drinking water out of a glass
VH-studio / Shutterstock

Drinking plenty of water is great for your body: A recent study linked good hydration habits with living longer and developing fewer chronic health problems. Sure, you've got lots of beverage options when you're thirsty (although you may want to skip the diet soda), but water is the best choice you can make for your health. Going even one day without drinking water can result in dizziness, fatigue, digestive problems, and more.

Still, it's important to take precautions when it comes to the way you drink water. One of those, doctors say, is making sure you're not exposing yourself to harmful bacteria and inadvertently raising your risk of illness by drinking out of a dirty glass.

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It's not unusual to drink out of the same water glass for multiple days.

woman drinking from a glass of water.
fizkes / Shutterstock

Whether you use a refillable water bottle or prefer to drink out of a regular glass, not washing it between fill-ups is a widespread practice, doctors note. "Reusing the same glass without washing it is common in many households," says naturopathic primary care physician Devin Stone, ND, health advisor at biōReigns. "Sometimes the ease of just refilling our glass comes before thinking about the hygiene concerns related."

But some fairly gross things can happen if you're in this habit—and once you know about them, chances are you'll be scrubbing your water glasses a lot more often.

Using the same water glass without washing it can make you sick.

Man on couch feeling nausea

"If you use the same glass for a week without washing it, bacteria will begin to grow on the surface of the glass," Peter Michael, MD, Chief Medical Officer of VUE, tells Best Life. "It's important to frequently wash glasses to prevent this buildup with soap and water, not just water alone."

What if you finish the water and fill it up again? Will that keep you safe from bacteria? Trinh says no. "Even if you are refilling the same glass with fresh water, any bacteria present can multiply quickly and become dangerous," he explains, citing norovirus as just one of the more unpleasant viruses that can live on an unwashed water glass. And Stone says over time, that bacteria can create a colony called a "biofilm."

"Without washing and scrubbing these glasses, the bacteria stay harbored within the film, giving them the opportunity to replicate and expand in numbers," Stone states. "This leaves us exposing ourselves to unwanted microbes."

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Leaving a glass of water out can cause problems, too.

Senior man lying on bed with glass of water on the nightstand
cunaplus / Shutterstock

Even if you do wash your water glass regularly, leaving water sitting out can be problematic, according to all of the doctors we spoke with. "A glass left out in open air may be exposed to airborne bacteria from dust particles or other sources," Trinh explains. For that reason alone, keeping a water bottle with a lid on your nightstand might be the best idea. (It will also prevent spills, for the accident-prone among us.)

Whatever container you use for your water, don't forget to replenish it with fresh H2O every day. "Bacteria can also grow in the water if it is not changed often in as little as a few days, so don't leave water uncovered next to your nightstand," Stone warns.

Elizabeth Laura Nelson
Elizabeth Laura Nelson is the Deputy Health Editor at Best Life. A mom and a marathon runner, she’s passionate about all aspects of health and wellness. Read more
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