If you examine a bottle of water, you may notice a couple of things: Claims that the water was drawn from a natural underground source, where it has been undisturbed for hundreds or thousands of years, and an expiry date informing you it will go off in January.
What is happening here? Is there something in the bottling process that turns the water bad, or are bottled water companies simply happening to pump water from underwater sources in the few months before it goes off?
Well, the answer is neither.
Does water expire?
Bottles of water do list expiry dates, but not because the water itself will expire. Expiration dates are printed onto the bottles at the same time as other information relating to the date of bottling, the bottling plant, etc, using the same machines that are used for other sodas made by the manufacturers.
As such, they will stamp water bottles with expiration dates rather than have a dedicated machine just for bottled water without an expiry date.
Another reason why expiry dates are on bottles is because of New Jersey. In 1987, the state passed a law requiring expiration dates on water bottles. Rather than have a special manufacturing process for bottles destined for New Jersey, it was easier to just print expiration dates on all bottles of water. The law was repealed a few decades later, but the practice of stamping bottles with the expiration date has continued.
Does bottled water go bad?
Bottled water will not go bad after the expiration date in the same way that other foods and drinks do. It doesn't contain proteins and sugars (assuming you aren't drinking sugar water with meat lumps) which get broken down by microbes, causing it to go "off".
However, it may begin to taste funny if it is left long enough, as chemicals from the bottle seep into the water.
"Bottled water is considered to have an indefinite safety shelf life if it is produced in accordance with [Current Good Manufacturing Practice] and quality standard regulations and is stored in an unopened, properly sealed container," the US Food and Drug Administration (FDA) writes on their website.
"Therefore, FDA does not require an expiration date for bottled water. However, long-term storage of bottled water may result in aesthetic defects, such as off-odor and taste. Bottlers may voluntarily put expiration dates on their labels."
Though the FDA deems it safe, if your water tastes odd after the expiration date you might want to give it a miss, to avoid any potential "forever chemicals", which have been linked in some studies to cancer.