"If you're ready for the zombies, a broken water line shouldn't be a big problem." Which reminded me of something Insty pointed to a couple of years back, and I finally found it: information on storing water.
Short version: bleach. Non- colored, non-scented, no soap, just bleach. They say 5.25% sodium hypochlorite, but most of the stuff I find is 6%, which seems to work just fine.
And this time of year, I think about it; tornados or windstorms or hail or a downburst can just ruin the day for electrically-driven stuff for a few days.