Considering your body naturally dehydrates overnight, it’s not uncommon to wake up thirsty.
But should you be drinking that glass of water you left on the nightstand last night, or even the night before? That’s up for debate.
If your water was left in an open glass, it’s obviously not the most sanitary. Dust, debris, and even casual bypassing bugs can drop into the glass overnight, leaving you with unhealthy surface scum.
Even closed containers aren’t safe. Our skin is covered in sweat, dust, skin cells, and even some nasal discharge (sorry we’ve grossed you out, germaphobes), so once our mouth first hits the bottle, you’re ‘backwashing’ all that good stuff into the water. Saliva carries bacteria, too, contaminating the water in the same way.
“If it’s allowed to incubate for hours, that could potentially contaminate the water, and make you ill by reintroducing that bacteria,” says Marc Leavey, MD, primary care specialist at Mercy Medical Center in Massachusetts. “Once you have put your lips to the bottle, you should consume that bottle in one sitting and then discard it.”
Related: Four Ways to Make Water Less Boring to Drink
This begs the question: Could you get sick from drinking a glass of water that has been sitting overnight?
Well, since it’s your own bacteria, the likelihood of actually getting sick is relatively low. Many people sip from used drinking glasses, mugs, and bottles without any ill effects.
Having said that, you probably shouldn’t be sharing any bottles, open or closed, otherwise. People with a reduced immune system, such as transplant patients, those undergoing chemotherapy, or people living with HIV/AIDS, should be extra wary of contaminated water, too.
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