Expiration dates on non-perishable consumer goods are a funny thing. Few people need an explanation as to why meat or dairy products have a sell-by date, but other things seem to demand a little more context. Child car seats, for example, have an expiration date because safety regulations change on a regular basis and because they can experience wear after years of daily use.

A date stamped on bottled water, however, seems to defy all laws of common sense. Shouldn't H2O technically be good forever?

The answer is yes—but water quality isn't the issue. A 1987 New Jersey state law required all food products sold there to display an expiration date of two years or less from the date of manufacture. Labeling, separating, and shipping batches of expiration-dated water to the Garden State seemed a little inefficient to bottled water producers, so most of them simply started giving every bottle a two-year expiration date, no matter where it was going.

The U.S. Food and Drug Administration has never established or suggested a limitation on the shelf life of bottled water as long as it's produced in accordance with regulations and the bottle remains properly sealed. New Jersey caught on to this fact and amended the law, but the expiration date has been an industry norm for so long that many producers have just kept it on there.

While "expired" unopened bottled water isn't going to do you any harm, it isn't going to get better with age, either. The plastic that water is packaged in—usually polyethylene terephthalate (PET) for retail bottles and high-density polyethylene (HDPE) for water cooler jugs—may begin leaching into the liquid, affecting its taste. It's also slightly porous, so the water can pick up smells and other unwelcome additives from the outside world. The odds of a five-year-old bottle of Evian harming you are virtually nonexistent, but if it's been stored in your basement, you might be better off reaching for a fresher bottle.

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