re: non potable water....for hurricane use I fill a 33 gal plastic trashcan in my single bath shower to use for bathing and flushing.. that way I have access to the shower's drain, and still room to stand... an additional 33 gallon can is placed at the end of my eaves where I knock out the end cap

my water heater holds heat over for about 2 days, so warm showers are still available for a time... don't overlook the water heater as a storage tank... make sure the tank drain is not covered with silt... a short piece of hose can make access much easier