Buzz
We’re all familiar with how food and drinks can spoil. Chances are, your fridge contains items that were once fresh but are now past their prime, unfit to eat. But one essential part of life that seems immune to this spoilage is water. After all, it’s just a simple compound made of hydrogen and oxygen, with nothing in it for microorganisms to contaminate. It makes sense when leftover chutney goes bad, but water seems so invulnerable that an expiration date on a water bottle might seem absurd. However, it’s not entirely incorrect. While water doesn’t rot or decay like food, it still has a limited shelf life.
When Tap Water Turns Bad
The water flowing from your tap has likely been treated with chlorine, which keeps harmful microorganisms at bay. However, over time, the water interacts with carbon dioxide in the air, lowering its pH and making it more acidic, which can result in a strange taste. Additionally, open water will collect dust and other particles from the environment, further diminishing its quality. In the long run, this process could even make you sick, though it would take a very long time for the water to become dangerous rather than just unpleasant.
Meanwhile, the chlorine added to tap water is off-gassing and gradually dissipating, which makes the water more appealing to microorganisms. The bottom line is that a glass of tap water left out overnight might taste odd, but from a health standpoint, it is probably safe to drink. However, if water sits out for an extended period, it’s best to avoid it—especially if there are visible signs of things, you know, living in it.
When it comes to storing water, as a general guideline, tap water can be stored for about six months in sanitized, food-grade containers. After that time, the chlorine treatment loses its effectiveness, and even small amounts of impurities can start to develop. This applies to filtered water as well. Though the filter may remove harmful substances, once the water is exposed to the air, these processes begin, eventually resulting in water that may taste bad or even cause illness.
When Bottled Water Spoils
Bottled water lasts longer than exposed water, but it will spoil eventually. The water is initially pure when bottled, and the plastic (mostly) keeps microorganisms out—but the plastic itself becomes the issue. The plastic isn’t completely impervious, so the water will gradually interact with the air, evaporating and creating a slight, but not negligible, risk of contamination. More importantly, chemicals from the plastic can seep into the water, a process accelerated by heat and sunlight. While these chemicals can be harmful in large quantities, there likely won’t be enough to cause harm from an old bottle of water, though the taste may suffer. This is why aged bottled water sometimes tastes like plastic.
As a general rule, bottled water remains good for about two years if kept sealed and stored in a cool, shaded location. Once the bottle is opened, however, the clock starts ticking faster because you’re now part of the equation. The moment any part of your body—lips, fingers, or otherwise—comes in contact with the water, you introduce microorganisms into the bottle. Over time, these organisms can multiply, which is why reusing a dirty glass or water bottle without cleaning it leads to unpleasant, potentially harmful water. Leaving bottled water open and exposed to the air sets in motion the same degrading process that affects tap water.
Entropy is the inherent nature of the universe—and that includes water, which may seem harmless. Over time, like everything else, that glass of water on your nightstand will eventually go bad.
