Emergency water planning becomes much easier when you turn household size and duration into a number. CDC guidance says to store at least one gallon per person per day for at least three days, with more where possible.
Emergency water calculator
What the one gallon baseline covers
CDC describes the stored supply as water for drinking, cooking, brushing teeth, and other emergency uses. It is a minimum planning baseline rather than a prediction of normal household consumption. Hot weather, pregnancy, illness, physical activity, pets, and special medical needs can increase requirements.
Three days versus a longer disruption
A three day reserve addresses the immediate emergency. Longer disruptions change the problem because storing every future gallon becomes bulky. This is where a replenishment layer becomes useful. Depending on your location and circumstances, that might mean a safe alternate source, rain capture, or atmospheric water generation.
| Household | 3 day human baseline | 7 day human baseline | 14 day human baseline |
|---|---|---|---|
| 1 person | 3 gallons | 7 gallons | 14 gallons |
| 2 people | 6 gallons | 14 gallons | 28 gallons |
| 4 people | 12 gallons | 28 gallons | 56 gallons |
Build layers instead of betting on one source
Start with stored water. Add a treatment plan for appropriate alternate sources. Then evaluate replenishment such as rainwater and water from air.
Our Water Freedom System review examines the DIY guide through climate, energy, treatment, and total project commitment.
Read the buyer focused review- CDC, How to Create and Store an Emergency Water Supply, updated June 2025.