Pfft... So that you will believe that you need to buy more after a certain date and that water goes bad...*loves marketing manipulation* :)
Enlightened you are... :)
Pretty sure it has to do with laws governing consumables. Some (if not all states) mandate an expiration date of some kind.<br />
Plastic is porous to a degree too, which may be a factor.
It can go back because it's in a plastic bottle. Plastic has chemicals that can effect water after awhile, especially when exposed to sunlight. Or at least, that's what my mom says.
It might be filtered, but it isn't distilled, so there's still some things in it. Plus there plastic in the bottle deteriorates, so i guess that can add chemicals to the water over time
idk... it starts to taste plasticly and then well it sorta taste coconut like to me :D