Many people like pouring a glass of water for their bedside at night — but is there anything wrong with drinking that same glass the next morning? What about that half drank bottle of water in your car cupholder?

Of course, most people don’t think twice about drinking day old water from a clean source. Our bodies tend to become dehydrated as we sleep at night, and it’s not uncommon to reach for the remainder of that cup of water when we first wake up. But what’s the difference between fresh poured and older H2O?

tasting Fresh vs. stale water

Anyone who drinks water — that’s everyone lucky enough on Earth — could tell you that water that has been left out has a different taste to it. It’s not dissimilar to other beverages: When you leave soda out it goes flat; when you leave wine out the flavor changes.

When water sites out, more carbon dioxide can get into it. This ultimately forms carbonic acid which lowers the pH balance and can alter the taste.

The amount of chlorine also plays a role in the taste of water from one town to another. Leaving water out a while can cause some of that chlorine to evaporate resulting in a different taste.

But we already recognized that the taste was different. Is it safe to drink?

Safety

Technically, water that has been left out is safe to drink — but there are a few considerations.

Besides the chemical composition changing slightly, you also need to consider dust and debris — there is more  floating around in the air than you care to think about. Bugs can also drop inside and contaminate your cup, and while you would think you would notice, consider how alert you are first thing in the morning and whether a teensy speck at the bottom of a cup in a dimly lit room would get your attention.

Even your own bacteria adds to the ‘ew’ factor of second day water. When you drink from a cup, your saliva leaves behind bacteria. Since it’s your own, you’re likely to be unaffected by it, but if left out for multiple days could do more harm.

mug shot

The takeaway? It’s not the water that is likely to cause you harm. It’s the bottle, glass or mug that you put it in. This is the surface area that bacteria will breed. While bacteria can breed it water, it’s mostly the cup that should get your concern. So if you’re one of those people who leaves a water cup out on your desk for days constantly refilling it, you should seriously reconsider.

when it’s in the car

While a lid might keep debris and bugs out of your car water bottle, there is something different to worry about. When a plastic bottle is exposed to sunlight, as it is in your vehicle, it can release estrogen-like chemicals such as BPAs. There is some controversy surrounding what constitutes toxic levels of BPAs, but when health is at risk, it’s best to take precautions and grab a new bottle — or better yet, fill up your own glass or BPA-free water bottle and help the planet while you’re helping yourself.


Also see, This is what would happen if you stopped drinking water. 

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Author

Meghan is a full-time writer exploring the fun facts behind food. She lives a healthy lifestyle but lives for breakfast, dessert and anything with marinara. She’s thrown away just as many meals as she’s proud of.