Technically, the water inside a sealed plastic bottle can last indefinitely. Water itself doesn’t spontaneously go bad—it’s just H₂O. But here’s the twist: the plastic bottle is the real timer, not the water.
Manufacturers put an expiration date on the bottle (usually one to two years) for legal and taste reasons. After that, the water might still be safe, but it could start tasting like a plastic bag that just ran a marathon. Why? Because over time, tiny bits of the plastic can leach into the water, giving it that weird, flat, slightly chemical flavor.
