WW3 WW3 PREP / FIELD LIBRARY
How much emergency water do you need?
Calculate a household emergency water baseline for 3, 7 or 14 days, with a transparent formula and source.
The calculation
This planner uses 3.8 litres per person per day, rounded up from one US gallon. Multiply people × days × 3.8. Four people for three days gives 45.6 litres; the shopping total rounds up to 46 litres.
What the number means
CDC guidance uses at least one gallon per person daily for drinking and other essential uses, for at least three days. Needs can be higher in heat, illness or pregnancy. Add pet needs separately. This is a storage baseline, not a prescription for how much anyone should drink.
Count the supply you already have
Enter your usable stored water to see the shortfall. The calculator does not check container safety or expiry. Review those yourself before counting a bottle as available.
Store and review
Follow the CDC storage guide linked below. For commercially bottled water, check the expiry information. Keep the total practical: a home reserve is not the same as water you can carry during evacuation.
Primary source
CDC — Emergency water supplyRead the full instructions and your local official guidance. References accessed 3 October 2026. No independent expert review.