Expiry dates on bottled water

I'm sure at least one of you out there has baught some crappy bottle of water because of the little graphic on the bottle and the promise that this water is awesome!

an example:

<insert name> is filtered naturally through volcanic micro porous rocks over millions of years, which gives it its different taste.

expiry date: tomorow.

The hell? its already millions of years old, how can we justify slapping an expiry date on it?

The mind boggles.

It shouldn't be just because its been bottled, could it? - most of this water moves incredibly slowly.

No doubt its a marketing ploy.