Can bottled water go bad? Of course not. Water is water now and 10 years from now. However, there is still an expiration date on the bottles of water we drink. Why?
The main reason for this is government bureaucracy. According to the laws in most countries, all consumable food products need to have an expiration date on the package. Bottled water falls under this category so it has an expiration date, but there are other reasons as well.
The plastic bottles that are filled with water can expire and they can start leaching chemicals into the water. This does not necessarily mean that the water will become toxic, but it might change its taste (and not for the better). So, if someone complains to the drink company that the water does not taste fresh, they can point out that the water should be drank before the expiration date.
On the printed code along with the expiration date, there are also details like when was the water bottled, in which plant etc. The manufacturing information could be useful in tracking down contamination, bottling errors or product recalls.
We also need to take into account that many companies use the same machines to bottle other kind of drinks which do have a real expiration date, so it’s easier and more efficient to put a code stamp on all bottles rather than to have special machines just for the bottles of water.