This is not because it will go bad but because some countries have laws requiring expiration date to liquids. Also, people know how long back it was packed. However, plastic bottles will gradually release volatile molecules from the plastic. Most of these will escape into the air, but some of them will get in water. It is difficult to taste them and not certain as well if they would accumulate over time instead of being reabsorbed in the plastic once they reach the equilibrium levels in the water.
Why is it important to write an expiry date on bottled water?
