- Ready.gov guidance is one gallon per person per day, for drinking and sanitation.
- A household of six for 90 days needs 540 gallons at that minimum.
- Stored water is a reserve; a well or cistern is a supply.
The math
| People | 14 days | 90 days | 180 days |
|---|---|---|---|
| 4 | 56 gal | 360 gal | 720 gal |
| 6 | 84 gal | 540 gal | 1,080 gal |
| 8 | 112 gal | 720 gal | 1,440 gal |
| 12 | 168 gal | 1,080 gal | 2,160 gal |
| 16 | 224 gal | 1,440 gal | 2,880 gal |
That is the minimum for drinking and basic sanitation. Cooking, washing up, showers and laundry all add to it, and so do hot weather and hard work.
Where it goes
Water is heavy, about 8.3 pounds a gallon, and it takes room. Tanks under the floor, a dedicated food and water cube, or a buried cistern outside the bunker keep it from crowding the living space.
Where more comes from
Stored water runs out. For a long stay, plan a source: a well with a hand pump, a cistern, or rainwater. In much of the West, using groundwater or surface water requires a water right, so check your state's rules before counting on a new well.
Questions
How long can water be stored?
Store-bought sealed water keeps a long time; water you bottle yourself should be rotated. Follow the date on commercial water and rotate home-filled containers on a schedule.
Does a CUBE Bunker include water storage?
The Water system is an add-on in the Builder, with tanks sized for your household, and a food and water cube gives it its own room.
CUBE Bunker prices are preliminary until engineering for the cube system is complete and are confirmed in writing after a site visit. This guide is general information, not engineering, legal or medical advice. Updated 2026-11-02.