The simple answer is that some states mandate that all food and drinks packaged and sold commercially have one. (Related: Bottled water is up to 3,500 times worse for the planet than tap water.)
Many bottled water companies print a standard two-year expiration date on their products. However, this number is arbitrary as there is no precise way to predict when the water in the bottle will no longer be good to drink. In fact, the Food and Drug Administration (FDA), which regulates the bottled water industry, does not require a shelf life for bottled water to be designated.
That said, it stands to reason that the longer the bottle has been in circulation, the more likely it is to be exposed to heat or start to degrade.
The quality of bottled water can depend on several factors. In fact, a brand new plastic bottle that has been sitting in a hot delivery truck for hours can be more dangerous than water stored in a cool place. This is because heat can degrade the plastic, leaching chemicals into the water.
As a general rule, as long as you drink the water reasonably soon after you buy it, or if you don't expose it to any long-term heat, your bottled water should be perfectly safe.
Bottled water does not go bad, strictly speaking, but storing it for a long time can result in noticeable changes. Even without heat, chemicals from the plastic bottle still start to seep in over time. This will give the water an unpalatable taste, but it does not necessarily mean that it is not safe to drink.
However, opened or unsealed bottles may be a bit problematic, especially if you took a drink before putting it away. Water that has been opened may be contaminated with microorganisms, from bacteria to algae.
The rule of thumb is that you should consume or dispense with "opened" water within two weeks to avoid having microorganisms bloom in the container. Bacteria, for instance, will multiply fast in water if conditions are right. Some bacteria can be dangerous and can make you sick.
Algae is mostly harmless, but it will create a nasty-looking and occasionally foul-smelling goop in your water vessel.
The takeaway here is to only ever open your bottles when you need to drink and to avoid storing any opened bottles with water in them for long periods of time.
Even if bottled water does not necessarily have a set expiration date, proper care must still be taken when handling and storing it.
Here are some tips you can follow to store your water bottles properly and safely.
Learn more about how to keep your water supply clean and free from contaminants at CleanWater.news.