Why Does Water Get Stale?
If you’ve ever kept water by your nightstand, you’ve probably noticed that your water tastes weird after taking that spent-to-long-sitting-out sip. But perhaps weird is the wrong word, as that implies the water is bad for you. Maybe a better phrase would be “stale.” So what’s up with that? Why does our water get stale?
The Most Likely Culprit
One of the most probable culprits for our stale shenanigans is just room temperature. Nobody really drinks warm water (right?)–most people are probably used to water being cooler than room temperature. Either we use ice, the cool end of the tap, or water simply makes things cooler (you know, the whole reason why we sweat).
When you leave water out for extended periods of time it eventually reaches room temperature. Because that’s just how physics works–everything wants to equalize. It’s quite a nice microcosm for how the universe will probably end. Everything just becomes a homogenous mix where literally everything is the same. We call it heat death, but we now want to call it “the universe becoming stale.”
Further Reading: When Will the Universe End?
Anyway, cooler temperatures generally kind of mask flavor profiles. There’s a numbing effect to it that we’re all just kind of used to, but probably never applied to our own taste buds.
So when our water (or other beverages) are at room temperature, we actually end up just tasting and smelling the “true flavors and aromas” of our glass. It’s kind of like when you let your soda de-bubble. It’s basically sugar-water at that point.
But Wait! There’s More!
It would be quite boring to learn that our water tastes weird just because it got mildly warmer. There’s also the fact that your water is pretty gassy. Gasses dissolve easier in water as it gets warmer. That’s just kind of how thermodynamics operates. Hotter means molecules move faster, and things just kind of get jumbled together.
Thus, gasses are dissolving in your water as it sits out un-sipped. Some of those gasses are carbon dioxide (what you breathe out), and as that dissolves in your water, it lowers the pH value of it. That is to say, your water is getting more basic.
For a point of reference, the pH scale goes from 1 to 14, with 7 being neutral. The lower the number, the more “acidic” something is, and the higher it is, the more “basic.” Your blood sits around the 7.3-7.4 mark, and rain across the American Midwest and Pacific Northwest sits comfortably around 5.2. Approaching the East Coast you start seeing rain around pH 4.5, in case you were wondering.
If you want to go taste something acidic right now, lemons enjoy a nice pH of about 2.
So carbon dioxide floating around in the air is getting in your water and making it more basic. That’s why water you keep in the fridge or in a bottle gets stale slower.
More On Gas
Of course, the water we drink has stuff in it. From fluorine to chlorine to ammonia treatments to an acceptable amount of lead that is not zero. Though in America we’ve got issues meeting that standard anyway, see the Flint Water Crisis.
But unless your municipality has widespread water issues, you’ll probably be fine with the stuff both in and out of your water.
The point is, if some gas is going to go into the water, some will also come out. Water’s not going to be hogging everything without giving some back.
Anyway, stuff like chlorine is going to be leaving your water–it’s pretty prone to doing stuff when left alone. Because we’re used to it, we kind of conflate the stuff in our water that isn’t straight dihydrogen monoxide with “fresh water.” So when it’s not there, it just tastes wrong. That also depends on where you live, some places treat their water with way more stuff than others.
Here’s a fun trivia fact: people have called water “dihydrogen monoxide” before and freaked people out. Yeah, being scared of water probably wasn’t the high point of the human race.
Get ready to dip your toes in more water trivia here.