Question:
Had some gallons of commercially bottled spring water that my wife insisted I buy after September 11. My daughter told her that if she insisted on buying bottled water to drink daily, then buy the gallons and refill the small ones. So I dragged out the gallons. I noticed that they had all passed the expiration date. How the hell does water go bad?

Answer: The water didn't go 'bad'. The date on bottled water is more of a 'best if used by' rather than 'expiration' date. Some of the minerals may have dissipated over time but the water is perfectly fine to drink.

It leaches out chemicals (mostly the smaller plasticiser molecules and some inorganics) from the plastic. Usually doesn't taste very good. Also the water probably wasn't sterile to begin with and may have a substantial bacterial load after all that time.