We once laughed at bottled water with expiration dates on it. And, to be honest, we used to laugh at the whole idea of bottled water, before schools removed their water fountains and Flint's water system collapsed. But water doesn't expire, does it? No. What expires is the bottle. A bottle's expiration date is the estimated date at which chemicals leeching from the plastic bottle could affect the taste of the water.
However, there is no legal requirement to pull expired water from store shelves. The chemicals that affect taste are not in high enough concentrations as to be dangerous. But that's only true if the water bottles have been stored properly. Heat, light, and other factors can cause problems in bottled water over time. Learn the factors that might make your bottled water unsafe and what to do about them at ScienceAlert:
Every bottle sheds chemicals a little bit, just by virtue of being in contact with water. Some of these chemicals are more toxic than others, such as antimony, a chemical that can damage your stomach and intestines, and phthalate esters, which can disrupt your endocrine system.
Hot water, you may remember from high school chemistry class, can dissolve larger amounts of chemicals than room-temperature water.
Research shows PET bottles heated past 86 degrees Fahrenheit can release an excessive amount of phthalate esters. Bottles heated past 140 degrees Fahrenheit can release dangerous levels of antimony.
(Image credit: US Navy)