Everyone always tells you to “drink more water,” but sometimes you end up with five half-full glasses of water sitting around the house in random places and then what? Is it okay to drink a glass of water after it’s been sitting around for a while? Reader’s Digest has the answer.

Apparently, it’s not necessarily a great idea to drink water that’s been left out, even just overnight. If you often keep a glass of water by your bed to drink when you wake up, take note! Dust, debris, bugs, and plain ol’ bacteria can all get into the water. Even sealed bottles of water are subject to contamination.

“If it’s allowed to incubate for hours, that could potentially contaminate the water, and make you ill by reintroducing that bacteria,” Marc Leavey, MD told Reader’s Digest. “Once you have put your lips to the bottle, you should consume that bottle in one sitting and then discard it.”

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Fortunately, the likelihood of you actually getting ill from your day-old water is pretty low — as long as you don’t share your cup or bottle with someone else. If your own bacteria is the main thing contaminating your water, you’re probably fine. However, people with compromised immune systems should be more careful.

Also, it’s not a great idea to drink water that was left in a hot place, like your car or the sun, especially if it’s in a plastic bottle. Chemicals from the water may leech into the bottle, plus all that heat is a breeding ground for bacteria.

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So, now you know: those day-old glasses of water lying around are probably safe to drink. So, no excuses: Drink more water.