Welcome.

As far as home water is concerned Izzy hit it right on the head. One thing to consider from personal experience, if your at home when a disaster comes and your bugging-in, fill your bathtubs with water and some extra 5 gallon buckets from the lumber stores.

A tub will give you about 40-50 gallons of water and since its in your pipes it won't be contaminated. You can ration this for hygiene, drinking and food prep. Then save the grey water. If you practice tonight you will know how much water it takes to flush your toilet by pouring this grey water into it, usually a couple liters. Then you can know you can flush your toilet once or twice a day with it.