Emergency water storage calculator

How it works

We multiply the people in your household by 1 gallon per person per day, then by the number of days. Adults and children count the same, because the figure is per person. Pets are added on top. Amounts are rounded up, and containers are rounded up to whole containers.

What a gallon covers: Ready.gov says the gallon is for drinking and sanitation. It also says a normally active adult needs about three-quarters of a gallon of fluid a day, from all drinks, so most of the gallon goes on drinking.

How many days: the CDC says at least 3 days, and about 2 weeks if you can. Ready.gov says several days and no longer names a number.

Hot weather: Ready.gov says water needs can double in very hot temperatures, so the hot-weather option doubles the amount for people. It's an upper planning figure. Children, nursing mothers and sick people may need more, and neither agency gives amounts.

Pets: no federal source gives a volume. We use 1 liter per pet per day, about a quarter of a gallon, which is the figure the Prep app starts with. It's an estimate. A large dog may need more and a cat much less, and it doesn't change in the hot-weather option.

Storing it: keep store-bought water sealed in its original container and follow its expiration date. If you fill your own food-grade containers, replace the water every 6 months. To clean a container, the CDC says to wash and rinse it, then add 1 teaspoon of unscented bleach (5–9% sodium hypochlorite) to 1 quart of water, shake so it coats everything, wait at least 30 seconds, pour it out, and let it air-dry.

Example: two adults, one child and a dog over 3 days is 9 gallons for the people and about 0.8 for the dog, 9.8 gallons in all. That's 10 gallon jugs, or 2 of the 5 gallon containers.