Last reviewed 30 October 2026
One gallon per person per day. That is the FEMA minimum, covering drinking and basic sanitation, and every family figure is just that rule multiplied by people and days. A family of four needs 12 gallons for 3 days, 56 for two weeks, 120 for a month (run your own numbers). In heat, plan on more — very hot conditions can double drinking needs, and this site's calculator plans hotter-climate households at 1.5 gallons per person per day by default.
The numbers, by family size
At 1 gallon per person per day:
| Household | 3 days | 14 days | 30 days | 90 days |
|---|---|---|---|---|
| 2 people | 6 gal | 28 gal | 60 gal | 180 gal |
| 4 people | 12 gal | 56 gal | 120 gal | 360 gal |
| 6 people | 18 gal | 84 gal | 180 gal | 540 gal |
Don't forget pets: a dog drinks roughly an ounce of water per pound of body weight per day, so a 50 lb dog adds about half a gallon a day.
You don't have to store all of it
Storing a full month of water means finding room for 120 gallons, and most homes can't. The workable strategy: store two to four weeks' worth, and cover the rest with collection and purification — rain barrels where legal, a gravity filter, purification tablets, and a pot and stove to boil. That stored-plus-gap approach is what the calculator on this site plans around, and it shows you the size of your gap at each stage.
Containers and rotation
Food-grade containers only, filled from the tap and sealed, keep about six months before they should be refreshed; commercially bottled water keeps longer. Store containers inside the cooled part of the house, off concrete floors, away from chemicals and gasoline fumes, which can permeate plastic over time. Five-gallon jugs are the practical unit — a full month's drinking water for one person is six of them.
The mistakes that matter
Storing water in a hot garage (heat degrades containers and encourages growth), counting the water heater and toilet tanks as your plan without knowing how to drain them safely, and — the big one — storing food that needs water (rice, beans, freeze-dried meals) without counting the cooking water in your total. Your food plan and water plan are the same plan.
Sources: Ready.gov — Water · Ready.gov — Build a Kit
Get your household's exact water figure — total need, what to store now, and the gap to purify — with the free DayCount Supply calculator.
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