You know the feeling. You filled up a glass of water the night before, you crawl out of your bed, and you get up and start your day. You find your glass of water sitting on your desk and decide to take a small sip (you might have heard that drinking water first thing in the morning jumpstarts your metabolism and resets your digestive system). You recoil in disgust. Why is that your water tastes so… what’s the word? Stale?

And it’s true. Scientists have found that water does indeed taste stale after being left out for a night and there are two chemical reasons behind the odd flavor.


water tastes

Photo by Caroline Liu

The temperature of your water has a significant effect on the taste of your water. The chances are that you poured that glass of water from your cold Brita filter and drank a small sip of refreshing water. The next morning? That water was probably room temperature and just didn’t taste as refreshing.

Even though the cold refreshing water may taste better, the room temperature water helps aid digestion and maintain high energy levels better. If you’re looking to lose weight on the other hand, drinking a glass of cold water has been found to boost your metabolism and can lead to an extra caloric burn of 70 calories.

The point is, however, that room temperature water just doesn’t taste as refreshing and crisp as cold water. This could lead to that “stale” taste in your mouth in the morning.

Dissolved Gases

water tastes

Photo by Sayuri Sekimitsu

The real reason for that stale taste in your water, however, is the gases that dissolve in your glass of water. This is why if you have a closed water bottle, you don’t have the same problem. Especially as the water temperature approaches room temperature, the solubility of the water increases. Simply put, solubility is a measure of how easily gases dissolve in a liquid. As temperature increases, solubility increases.

All of this means that different types of gases are dissolving in your water overnight. These gases include carbon dioxide and even aldehydes and acetone. The amount of carbon dioxide that dissolves increases the acidity (or lowers the pH) of your water which explains the weird different taste of your water now.

Although that was a lot of chemistry (o-chem anyone?), it’s nice to finally know the reason for your stale water. How do we fix this problem? Get a water bottle and stick your water bottle in the fridge overnight. That way you can wake up with refreshing water in the morning (hello, metabolism boost). Or, if you want that digestion aid, just make sure to cover your glass of water with a cap to reduce the amount of dissolved carbon dioxide in your glass of water.