I gotta ask....If you're on town water, as opposed to a well, do you go get bottled water, and, if so, why?
We're on town water here, and we don't drink it, even when there isn't an emergency. So we keep a good deal of bottled water on hand anyway.
Also, there's no guarantee that it will keep flowing. Watermains have issues occasionally. With a case of small bottles to be had for $3, there's no real reason NOT to, at the very least, keep some on hand.