|MadSci Network: Chemistry|
I've never come across bottled water expiring the same month I bought it and I don't know that it would be very refreshing if that is the case... but bottled water has an expiration date because over time, it tends to pick up off-flavors from its packaging. High storage temperatures also contribute to the generation of musty tastes in the water, so ideally, the manufacturers should label the water sold in warmer climates with shorter expiration dates (I doubt they do this because it is very difficult logistically). Anyway, there shouldn't be any microbial concerns with bottled water as long as its package hasn't been compromised.
Here are a few sites with more information from the International
Bottled Water Association:
Bottled water FAQs
And a few from other sources:
Drinking water in brief
Bottled water in Canada
Article with general info
I hope this information has helped!
Try the links in the MadSci Library for more information on Chemistry.