Emergency Water Storage Calculator
Calculate how much water to store for an emergency.
Based on the recommended minimum of 4 litres per person per day for drinking and basic sanitation.
Why water is the first survival priority
You can survive three weeks without food but only three days without water — less in heat or while doing physical work. Every emergency-prep authority puts water at the top of the storage list, ahead of food, batteries, or fuel. If you have to pick one thing to stockpile, pick this.
How much per person per day
The base recommendation is 1 gallon (3.78 L) per person per day for drinking plus minimal hygiene. The number scales with conditions:
| Climate / activity | Per person per day |
|---|---|
| Temperate, sheltered | 4 L (1 gallon) |
| Hot, mostly indoors | 6 L (1.6 gallons) |
| Extreme heat or physical labour | 8 L (2.1 gallons) |
| Children or nursing mothers | +50% on the above |
Pets need water too: about 0.7 L per day per medium dog or large cat, scaled by size. Small dogs and most cats settle at 0.4 to 0.5 L; large dogs (40 kg+) need closer to 1.5 L.
A 14-day baseline for 4 people
4 people × 14 days × 4 L = 224 litres (about 60 US gallons). That is:
- 4 × 55 L drums, or
- 12 × 20 L jerry cans, or
- 100+ standard 2 L bottles
Most households underestimate the volume. 60 gallons takes up about 8 cubic feet of floor space; a closet shelf will not fit it. Plan storage location before you buy the containers.
Container choices
- HDPE food-grade drums (the blue 55 L / 15 gallon kind): cheapest per litre, last decades. Heavy when full (55 kg).
- Stackable 20 L jerry cans: easier to handle, can be moved one at a time. Slightly higher per-litre cost.
- 2 L bottled water from the supermarket: convenient but expensive per litre, and the thin plastic degrades faster than HDPE drums.
- Avoid old milk jugs: HDPE thins over time and residual sugars feed bacteria. Not safe for long-term storage.
Treatment and rotation
Tap water is generally safe to store for 6 to 12 months in a clean food-grade container. After that, rotate and replace, or pre-treat with 2 drops of unscented bleach per litre and re-treat every 6 months. Boiling, water purification tablets (chlorine dioxide), and a quality filter (Sawyer, Berkey) all work as backup if your stored water runs out and you are drawing from a creek or rainwater.