Know exactly how much water your household needs to survive 72 hours. Enter your people count, activity level, and special needs — get your total in litres, gallons, and containers.
Starts at 3 days — raise the days for a longer home supply
Household & Duration
Adults
ppl
Children
ppl
Days
days
Activity
Special Needs (Optional)
⚠ Please enter at least 1 person and 1 or more days.
WaterTankCalculator.com — 72-Hour Emergency Water Results
Your Emergency Water Plan
Total Water Needed
—
Litres (L)
US Gallons
— gal
UK Gallons
— gal
Per Person/Day
— L/day
Drinking Water
— L
Sanitation Water
— L
1L Bottles Needed
— btls
2L Bottles Needed
— btls
20L Containers
— jugs
Water Weight
— kg
Supply Breakdown Visual
📖 How To Use
How to Use This Calculator
Planning your 72-hour emergency water supply takes under a minute:
Enter your household size
Count adults and children. Both get the full 1 gallon (3.8 L) a day — official guidance doesn't reduce it for children, and the gallon covers sanitation as well as drinking.
Set the number of days
The CDC's minimum is 3 days (72 hours) — the right size for a grab-and-go kit. For water kept at home, the CDC suggests a 2-week supply if possible, so try 14 days as well. The calculator accepts up to 30 days.
Choose your activity level
"Normal" uses the 1-gallon guidance as written. Choose a higher factor if you'll be active outdoors or the emergency may come in hot weather — Ready.gov notes that in very hot temperatures water needs can double. There is no option below 1 gallon, because that is already the minimum.
Add special needs (optional)
Add pets by size, and anyone pregnant, breastfeeding or ill with fever or diarrhoea. Each of those people gets an extra 1 L a day on top of their gallon — our planning allowance, in line with the extra fluid US National Academies intake values give for breastfeeding.
Read your results
The calculator returns your total in litres and gallons, split into drinking and sanitation, and how many 1 L or 2 L bottles or 20 L jerry cans to stock.
Tip: Store water in food-grade containers — sealed store-bought water is ready to use; follow its expiration date. Replace water you bottle yourself every 6 months (CDC). Keep containers cool (about 50–70 °F / 10–21 °C), out of sunlight and away from fuel or chemicals.
📐 The Formula
72 Hour Water Supply Formula
The calculation starts from the Ready.gov and CDC minimum of 1 US gallon per person per day:
Total Water = (People × 3.785 L + Extra Needs + Pets × Pet L/day) × Activity Factor × Days
Drinking & food ≈ 3 L of each person's gallon (top of the Sphere 2.5–3 L survival range)
Sanitation = the remaining ≈ 0.8 L per person per day
Pet L/day = (30 × body weight kg + 70) ÷ 1,000
US Gallons = Total Litres ÷ 3.785
UK Gallons = Total Litres ÷ 4.546
Daily Water Rates by Category
Person / Animal
Normal ×1
Active ×1.25
Hot ×1.5
Very hot ×2
Adult or child
3.8 L/day
4.7 L/day
5.7 L/day
7.6 L/day
Nursing/Pregnant (+extra)
+1.0 L/day
+1.25 L/day
+1.5 L/day
+2.0 L/day
Ill / Fever (+extra)
+1.0 L/day
+1.25 L/day
+1.5 L/day
+2.0 L/day
Cat / small dog (~5 kg)
0.22 L/day
0.28 L/day
0.33 L/day
0.44 L/day
Large dog (~30 kg)
0.97 L/day
1.21 L/day
1.46 L/day
1.94 L/day
These are minimums. For comfort and better hygiene, store more if you have room — 2 gallons (7.6 L) per person per day leaves space for cooking and washing. The heat factors between ×1 and ×2 are our planning steps; Ready.gov gives only the "can double" end point.
Critical: The FEMA standard of 1 US gallon (3.78 L) per person per day is a survival minimum. It covers basic drinking and minimal sanitation only. Children, nursing mothers and sick people may need more, and in very hot temperatures needs can double (Ready.gov).
🏠 When To Use
When You Need a 72-Hour Water Supply
🌊
Flood & Storm Events
Municipal water can become contaminated during floods. A sealed 72-hour supply ensures you have safe water even when taps are unsafe to use.
⚡
Power Outages
If treatment plants or pumps lose power, pressure can drop or a boil-water notice can follow. Homes on a private well lose water as soon as the well pump stops.
🏔️
Earthquake & Infrastructure Damage
Broken water mains after an earthquake can take days to weeks to repair. Keep at least 3 days in your kit and, if you can, the CDC's 2-week supply at home.
🚗
Emergency Evacuation
Bug-out scenarios require portable water. Knowing your household's daily requirement helps size your evacuation kit correctly.
🦠
Contamination Events
Boil-water advisories or chemical contamination of municipal water supplies can last days. Pre-stored sealed water is safe to use immediately.
🏕️
Off-Grid & Remote Living
Rural households relying on wells or rainwater collection need to know their daily demand to properly size storage and backup capacity.
🧮 Worked Example
Worked example: 72 hours for a family of four
Two adults, two children, one cat and one large dog, normal conditions, 3 days:
People: 4 × 3.785 L = 15.14 L a day.
Pets: cat (~5 kg) 0.22 L + dog (~30 kg) 0.97 L = 1.19 L a day.
Total: 16.33 L × 3 days = 49.0 L — about 12.9 US gallons, 3 × 20 L jugs (the last part-full), or 49 one-litre bottles. It weighs about 49 kg.
Split: about 36 L for drinking and food, 9 L for sanitation and 4 L for the pets.
If one adult is breastfeeding, add 1 L a day (3 L in total). In a heatwave (×1.5), the same household needs about 73.5 L for 3 days.
❓ FAQ
Frequently Asked Questions
How much water does FEMA recommend for a 72-hour emergency?
Ready.gov (FEMA) recommends at least 1 US gallon (about 3.8 litres) per person per day for drinking and basic sanitation, and the CDC says to store it for at least 3 days. For a household of 4 over 72 hours, that is 12 gallons (about 45 litres). It is a minimum — store more if you can, and add extra for pets.
How much emergency water does a family of 4 need?
At the official minimum of 1 gallon (3.8 L) per person per day for 3 days: about 45 litres or 12 US gallons. At 2 gallons per person per day, which allows for cooking and washing, it is about 91 litres or 24 gallons. For a 2-week home supply at the minimum, it is about 212 litres or 56 gallons.
How long can I store tap water for emergencies?
The CDC says to replace water you bottle yourself every 6 months, and to follow the expiration date on store-bought water. Use clean, food-grade containers sanitised with 1 teaspoon of unscented bleach per quart of water, fill them from a safe public supply, seal, label with the date, and keep them cool and dark. Treated tap water needs no additives.
How much water do pets need in an emergency?
A common veterinary estimate for dogs and cats of 2–70 kg is 30 mL × body weight in kg + 70 mL a day (MSD Veterinary Manual) — about 0.22 L for a 5 kg cat or small dog and 0.97 L for a 30 kg dog. Pets need more in heat or when active, so the calculator applies the same activity factor to them. If your pet is much bigger or smaller, use the emergency water storage calculator, which lets you choose the size.
What containers are best for emergency water storage?
Use food-grade containers with tight-sealing lids, such as HDPE (recycling code #2) water jugs. Commercial bottled water in original sealed packaging is the most convenient option. For bulk storage, 20-litre (5-gallon) food-grade jerry cans are practical for households. Never use containers that held chemicals, cleaning products or non-food items, and avoid milk or juice jugs — their residues are hard to remove.
Is 72 hours enough, or should I store more water?
72 hours covers most short-term emergencies (power outages, brief evacuations, storm events). However, major disasters — earthquakes, hurricanes, floods — can disrupt water supplies for much longer. The CDC suggests storing a 2-week supply if possible. Keep 3 days in a portable kit, and use this calculator with "14 days" for your home storage goal.
Do I need to include cooking and sanitation water separately?
The 1-gallon figure already covers both, but it is tight: if about 3 L a day goes on drinking and food, only about 0.8 L is left for washing and sanitation. The calculator shows that split. If you plan meals that need water (pasta, rice, soups), add extra — or choose ready-to-eat foods that need little or none. Don't ration drinking water to save it for other uses unless authorities tell you to.
How do I calculate emergency water storage for a hot climate?
Ready.gov notes that in very hot temperatures, water needs can double. Choose "Hot weather (×1.5)" for about 5.7 L per person per day, or "Very hot / strenuous (×2)" for about 7.6 L. Children and older people are especially at risk of dehydration in heat, so lean toward the higher factor if you have no way to keep cool.
✅ Sources & Review
Sources and review
The base rate is official preparedness guidance; the in-between heat factors and the extra-need allowances are our planning steps and are labelled as such.
Ready.gov (FEMA) — Water: at least 1 gallon per person per day for drinking and sanitation; children, nursing mothers and sick people may need more; needs can double in very hot temperatures.
Reviewed by John Mac, PE, Water Systems Specialist
Texas-licensed Professional Engineer with 13+ years in residential water storage and 180+ tank projects. John writes and reviews every calculator on this site.
