There is nothing in water that could possibly make it go bad or expire. Even in bottled water, the water itself could last forever without any negative consequences. So why are there expiration labels on plastic water bottles then? The bottle itself will start to expire before the water does. Expiration dates on plastic water bottles tell the consumer when the plastic will begin to break down, which leads to dangerous chemicals possibly leaking into the drinkable water. So yeah, those expiration dates are on water bottles for a reason.