Few people think of this, but just about everybody has an emergency supply of water already in place. Usually there is 30 gallons or so in the water heater, which can be easily accessed through its drain valve.
I think that's the only problem with the water heater solution, is it's not portable. You can't really bring it with you if you have to flee. Unless you had already drained it into smaller containers, of course.
As for wtc911's comment, I think that makes alot of sense. Going forward I think I'll pay even more attention to the storage of emergency supplies, making sure that they're split up in such a way that if one set is lost/washed away/burned up/stolen, another can sustain us for a little bit.
The best way I know, for me, to deal with catastrophes like this is to learn from them.