I was wondering why bottled water has a “drink by” date on it when common sense dictates that water doesn’t go bad, so I went out searching.
You can thank New Jersey, which passed a law in 1987 that 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 Jersey alone, was inefficient for bottled water producers, so most of them started giving every bottle a two-year expiration date, no matter where it was shipped to. Maybe that's also where Pepsi had inspiration for its "freshness date."
The U.S. Food and Drug Administration has never established a limitation on the shelf life of bottled water and even though the NJ law was amended a few years ago it has been an industry norm for so long that many producers haven't bothered to change.
Unopened bottled water may not do you any harm, but it isn’t going to get better with age. The plastic that water is packaged in, usually polyethylene terephthalate (PET) for retail bottles and high-density polyethylene (HDPE) for water cooler jugs, is slightly porous, so the water can pick up smells and tastes from the outside world. Keep a case in your garage for a while and your water might end up with a slick oil finish. Mmmm, bottled water - the pet rock of a new generation.