water in the bathtub? sure....all you have to do is boil it if it becomes undrinkable, or use condensation to purify it, condensed water is as clean as rain....scratch that...as clean as can be expected naturally.
ever see the omega man?? that would probably be the way to go, although those pesky zombies have a way of shambling through any real defenses somehow, or some snot nosed kid ruins the barriers for true love or a dog or something.