You need at least one gallon of water per person or small animal per day, more if you intend to be physically active. The rule used to be have enough for three days - I'd have enough for a week or more now. This one's *big*.
Pipes shouldn't burst. If the water cuts off, go dig a latrine outside, away from your home.
I think I have enough for about 3 days. My cat doesn't drink much, and I don't plan on moving around much if I am still here.