damned up stream is the key.
if you have your own creek or well all you need to do for the well is make sure the electricity works....if you have a generator, it'll work as long as you have propane or gas as fuel...
it its the creek, you'll definately need a filtration system.
but what is you are on county/ city water...it does not require a pump to bring it inside your house as I understand it so the only problem would be if the main source dried up or was contaminated....then you're out of luck unless you've stored a good amount away.....
would things be so bad that the army reserves wouldn't be out there handing out bottled water....