I've read a gallon per day is required; half for drinking, the other half for cooking and personal hygiene. The water may be off, but that's no reason to have Zombie breath! If you store five gallons per person, it will make those first few days of ANY emergency easier.
Trust me on storing water. You could drink the water from the toilet tank, but eww...
I have one of the containers on the left below that we take when we go camping, and three of the hard plastic containers in my storage room, filled and ready for the Big Day!
