Quick answer: Use one gallon per person per day as the baseline. The Red Cross lists three days for evacuation and two weeks for home supplies. Use that baseline for a household calculation, then address pets, hot conditions and individual needs separately. It is not a promise to cover normal bathing, laundry and toilet use.
Calculate people × days × daily allowance
| People | 3 days at 1 gallon/day | 7 days | 14 days |
|---|---|---|---|
| 1 | 3 gallons | 7 gallons | 14 gallons |
| 2 | 6 gallons | 14 gallons | 28 gallons |
| 4 | 12 gallons | 28 gallons | 56 gallons |
These figures are arithmetic from the baseline, before additions. One U.S. gallon is about 3.785 liters, so a four-person three-day baseline is about 45.4 liters. Do not mix a gallon-based target with containers labeled in liters without converting.
Count what is actually usable
Make a reserve ledger with container location, volume, fill or manufacturer date and next check. Add only the supply intended and suitable for drinking-water tasks. Keep non-drinking water in a separate list so a large toilet-water container does not accidentally inflate the drinking reserve.
For example, if four people need 12 gallons and the ledger contains eight usable one-gallon bottles, the baseline gap is four gallons. A filter is equipment, not another four stored gallons.
Identify additions without guessing medical quantities
Review additional needs for pets, hot conditions and individual care requirements with the appropriate guidance or care provider. Do not use a generic multiplier as an individualized medical water recommendation.
List each addition beside its reason. This makes later changes visible when a pet joins the household, people visit or the planned duration changes.
Check weight and transport separately
Water weighs about 8.34 pounds per U.S. gallon. Twelve gallons weigh about 100 pounds before containers; 56 gallons weigh about 467 pounds. A deep home reserve therefore cannot simply be assigned to one person’s evacuation bag.
Choose manageable units and storage supports appropriate to the actual load. If capacity or building suitability is uncertain, resolve that with the responsible operator rather than assuming any shelf or cabinet will hold the total.
Build a reserve you can maintain
Start by closing the documented short-term gap, then extend the duration where space, handling and rotation permit. Keep the ledger current rather than treating a completed shopping trip as proof of readiness.
Use the storage routine, the container checklist or the apartment layout for those separate decisions.