If you’ve ever taken a sip from a glass of day-old water, you’ve likely noticed that it tastes just a little bit different. And bottled water usually has an expiration date stamped on it, so does that mean that it goes bad?
The short answer: Not really…but you should still be careful.
According to the International Bottled Water Association, the Food and Drug Administration (FDA) has determined that “there is no limit to the shelf life of bottled water,” and the FDA also doesn’t require bottled water manufactures to include an expiration date.
The Centers for Disease Control and Prevention (CDC) also noted that in the case of an emergency, bottled water is the safest type of water to have available because it can be stored for so long, but it does need to be stored properly. The CDC recommends storing water in a cool, dark place and not breaking the seals on bottled water until you’re ready to drink it.
The CDC also explained that it’s important to keep bottled water away from poisons like pesticides and gasoline, because the plastic is permeable. They also recommend keeping it out of direct sunlight, because some plastics can release the chemical bisphenol A (BPA), which has been tentatively linked to several health issues including heart disease and cancer.
Are There Any Dangers of Drinking Old Water?
Dr. Kellogg Schwab, director of the Johns Hopkins University Water Institute, told TIME that there are risks, but they’re usually minimal. He explained that after you take a sip from a glass or bottle of water, you’re introducing microorganisms to the water. Those microorganisms can then multiply quickly, especially if the water is sitting in the sun. However, they likely won’t do much damage over a short period of time.
“If you have clean water in a clean glass, you’re fine for a day or two,” he said. He also added that most tap and bottled water has trace amounts of chlorine that help kill bacteria, keeping water safer longer.
The risky part is when you drink water that’s been sitting out for several days or is in a dirty glass. Julian Huguet of Discovery‘s DNews explained that after a few days, the bacteria in the water can reproduce and potentially become unsanitary. He added that what might be more disgusting is all the dust in the air that lands in the water, contaminating it with all kinds of germs.
“Again, it’s not the H2O breaking down and going bad, it’s just hosting other nastiness that’s spoiling the taste,” he said.
So Why Does Bottled Water Have an Expiration Date?
Huguet explained that although manufacturers are not required by law to include expiration dates on bottled water now, it’s likely just “a holdover from an old New Jersey law that has since been repealed because there’s no scientific evidence to support it.”
So while water itself doesn’t expire or go bad, it’s still a good idea not to drink water that’s several days old or has been in the sun for too long just to be on the safe side.