📅 Water Storage Days Calculator
Mode 1: How long does my tank last? · Mode 2: What tank size do I need?
Days of Supply
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Water Usage Reference by Scenario
| Scenario | Per Person/Day | Family of 4 / Day | Notes |
|---|---|---|---|
| FEMA emergency minimum | 1 gallon | 4 gallons | Drinking only; no hygiene |
| Drinking + cooking | 3 gallons | 12 gallons | Minimal hygiene (hand sanitizer) |
| Basic — no showers | 15 gallons | 60 gallons | Toilet + sink + cooking |
| Normal household | 80 gallons | 320 gallons | Includes showers, laundry, dishes |
| Full household | 100 gallons | 400 gallons | EPA / USGS average American use |
| RV / camping | 5–15 gallons | 20–60 gallons | Depends on hookup availability |
Days of Supply by Tank Size
| Tank Size | Emergency (4 people, 1 gal/day) | Drinking Only (4 people, 3 gal/day) | Normal Use (4 people, 320 gal/day) |
|---|---|---|---|
| 150 gallons | 37.5 days | 12.5 days | <1 day |
| 300 gallons | 75 days | 25 days | <1 day |
| 500 gallons | 125 days | 41 days | 1.5 days |
| 1,000 gallons | 250 days | 83 days | 3 days |
| 2,500 gallons | 625 days | 208 days | 7.8 days |
| 5,000 gallons | 1,250 days | 416 days | 15.6 days |
| 10,000 gallons | 2,500 days | 833 days | 31 days |
Emergency Preparedness Guidelines
- FEMA minimum: 1 gallon per person per day for at least 72 hours (3 days). This is the survival floor — drinking only, no hygiene.
- FEMA recommended: 2 weeks of water supply (14 days at 1 gal/person/day) for extended outages.
- Realistic household preparedness: 30 days at drinking + cooking level (3 gal/person/day) = 360 gallons for a family of 4. A 500-gallon tank with 75% reserve capacity covers this comfortably.
- Rural well users: Plan for the well pump being down (power outage, pump failure). 7–14 days at normal household use for a family of 4 = 2,240–4,480 gallons. A 5,000-gallon tank provides 15+ days at normal use.