i keep some jugs of water on hand for times when the power goes out. we haven't needed them yet, but in case of trouble they're better than nothing. in a pinch they'll also work as toilet flushing water.
when the power goes out the first thing i do is turn off the hot water heater and then get out a few buckets and drain the pressure off the water system and keep that water for flushing toilets. while i'm at it i also fill up my drinking water cup and a gallon or so of water for drinking besides all the other jugs of water i have on hand already. that's why as of yet i've not had to get into the water jugs themselves for drinking water.