The Possible Reason Water Tastes Different After Sitting Out For A Long Time

Ever notice that water tastes different after sitting out, and the longer it's been sitting out, the stranger it tastes? If you haven't encountered this phenomenon, consider leaving a glass of water on your nightstand this evening. Take a sip before bed and another when you wake up, and then see if you don't notice that it tastes slightly off, as Wired claims. 

As it turns out, water, which should be odorless and flavorless, undergoes various changes as it sits out exposed to the air. This puts it in the company of milk, which starts to go sour within as little as an hour of sitting out, according to U.S. Dairy. This is because as milk loses its refrigerated chill, it can develop bacterial growth. This is in contrast to wines, which improve in flavor when aerated from exposure to (and absorption of) oxygen, according to Wine Enthusiast Magazine

But with enough time, oxidation starts to work against wine as well, and basically, any beverage left out long enough will start to taste funky at some point — even water. 

Water doesn't actually rise to its own level

Just as temperature affects milk, it also affects water. Regardless of the temperature of the water when it was poured, as soon as it begins to rise or fall in the direction of ambient temperature, the taste of your water will become stale, according to Wired. And like wine, water goes through a breathing process as it approaches room temperature. As chemist Susan Richardson told Wired, the oxidation process releases oxygen and absorbs carbon dioxide from the air. This lowers the water's pH, according to dietitian Hari Lakshmi (via HealthShots), making the water more acidic, which affects the taste. Our palates are used to alkaline water but not overly acidic water. 

Lakshmi doesn't give credence to the popular belief that water changes taste due to the growth of microorganisms. However, if you took a sip or two of your water before leaving it out, then the reality is that you've introduced your microbiome to it. But since it's your bacteria, so to speak, it's not likely to harm you, according to Livestrong. But it could change the water's taste. Further, airborne contamination from germs and household dust is possible if you've left your water uncovered. So in the interest of caution, it might be better to go ahead and pour yourself a fresh glass.