Why You Probably Shouldn't Drink the Glass of Water You Left Out Overnight
Here's everything you need to know about why that glass of water you left out overnight tastes so bad, plus how to make you water taste better.
For many of us, filling up a glass of water before bed is part of our nighttime ritual. But do you notice that sometimes when you take a sip in the morning, it tastes a bit off? You can’t pinpoint what it is, but it’s definitely not as refreshing.
As it turns out, there’s a reason why this happens. We spoke to toxicology experts to learn more.
What Happens When Tap Water is Left Out Overnight
When tap water is left out overnight or for prolonged periods of time, it is exposed to the ambient air.
Air contains multiple gasses like oxygen, nitrogen and carbon dioxide, Dr. Kelly Johnson-Arbor, MD, a medical toxicology physician at National Capital Poison Center, explains. Exposure to air allows these gases, specifically carbon dioxide, to dissolve into the tap water. When we drink tap water that has been left out overnight, an enzyme in our bodies (called carbonic anhydrase) converts the carbon dioxide to carbonic acid. The increased carbonic acid is responsible for the bitter or "stale" taste of the water.
Related: What’s the Difference Between Seltzer, Club Soda, Tonic Water and Sparkling Water?
Evaporation and sedimentation also play a role.
Dr. Luz Claudio, PhD, Professor of Environmental Medicine and Public Health, Icahn School of Medicine at Mount Sinai, says, “My best guess is that when tap water sits overnight two main things might happen. The first is that some of the water evaporates, and the second is that some sedimentation may occur where any solids or heavier molecules might settle at the bottom of the glass.”
However, none of these potential changes in the water are likely to be harmful. "For that reason, I disagree with the premise that you ‘shouldn't drink it,’" Dr. Claudio adds.
How to Make Your Water Taste Better
Many people find that cold water tastes better than warm water.
Cold water increases saliva flow more than warm water does, and increases in saliva flow are associated with decreased thirst sensation, Dr. Johnson-Arbor states. Because of this, cold water is perceived as being more effective than warm water in relieving thirst.
Cold water relieves other sensations associated with mouth dryness, and is also more satiating than warm water. For these reasons, keeping water tasting cold is crucial, Dr. Johnson-Arbor adds.
It’s also important to become knowledgeable regarding potential contaminants. The Environmental Protection Agency provides a list of types of drinking water contaminants.
To make sure the tap water in your area is safe and free from toxic chemicals, you can check out EWG’s tap water database and enter your zip code.
Next up: New Research Shows Gas Stoves Could Be Leaking Toxic Chemicals—How Worried Should We Be?
Sources
Dr. Kelly Johnson-Arbor, MD, a medical toxicology physician at National Capital Poison Center
Dr. Luz Claudio, PhD, Professor of Environmental Medicine and Public Health, Icahn School of Medicine at Mount Sinai
Environmental Protection Agency: “Types of Drinking Water Contaminants”
