Enter your household size, expected outage duration, and climate conditions to get your precise emergency water stockpile in gallons, litres, and container counts.
Fill in your household details to calculate total water storage needed
Household composition
Adults
Children
Infants
Pets
Duration & conditions
Days
days
Climate
Activity
Medical needs, pets & units
Medical water (L/day)
Typical pet size
Primary unit
⚠ Please enter at least 1 person (adult, child, or infant) and a valid number of days (1 or more).
WaterTankCalculator.com — Hurricane Water Prep Results
Your Water Plan
Total Water Needed
—
Litres (L)
US Gallons
— gal
Litres
— L
UK Gallons
— gal
Per Person / Day
— L
×1L Bottles
— btls
×5-Gal Jugs
— jugs
Weight (full)
— kg
Weight (lbs)
— lbs
✅Meets the 3-day minimum.
Water Volume Visual
📖 How To Use
How to Use This Hurricane Water Prep Calculator
Get your personalized emergency water stockpile in under 60 seconds:
Enter every household member
Count adults, children, infants and pets. Every person, including infants, is counted at the full 1 gallon (3.8 L) a day — official guidance doesn't reduce it for children, and children, nursing mothers and sick people may need more. Pick a typical pet size so pet water is estimated by weight.
Set your outage duration
The CDC's minimum is a 3-day supply, and it suggests a 2-week supply at home if possible — a sensible target for hurricane zones, where power and water can be out for a long time after a major storm.
Choose climate and activity level
Hurricanes usually hit in hot, humid weather, often with no power for air conditioning. Ready.gov notes that in very hot temperatures water needs can double. The default is hot/humid (×1.5) with moderate activity (×1.15); cleanup work raises it further. The combined factor is capped at ×2.5.
Note any medical or special needs
If someone needs water for wound care, medication or medical equipment, enter the extra litres a day. Ask the care team how much — needs vary widely, and people on home dialysis should follow their dialysis centre's emergency plan.
Read your results
The calculator returns total litres, US gallons, UK gallons, bottle/jug counts, and total weight — everything you need to purchase and store the right amount.
Pro tip: Store water in a cool, dark place in food-grade containers. Follow the expiration date on store-bought water, and replace water you bottle yourself every 6 months (CDC). Label every container with the fill date.
📐 The Formula
Hurricane Water Prep Formula Explained
This calculator starts from the Ready.gov and CDC minimum of 1 gallon per person per day, then adds heat, activity, pets and medical water:
Per person (adult, child or infant): 3.785 L/day × climate × activity
Climate: mild ×1.0 · hot/humid ×1.5 · extreme ×2.0
Activity: sheltering ×1.0 · moderate ×1.15 · cleanup ×1.3 (combined factor capped at ×2.5) Pets: (30 × body weight kg + 70) mL/day × the same factor Medical: the extra litres a day you enter
Total = (People × person rate + Pets × pet rate + Medical) × Days
The per-person rate in the results is one person's daily allowance after the heat and activity factor. In the chart, about 3 L of each person's gallon is shown as drinking and food water (the top of the Sphere 2.5–3 L survival range) and the rest as sanitation; pet and medical water are shown separately. The ×1.15, ×1.3 and ×1.5 steps are our planning factors; Ready.gov gives the "can double" end point.
FEMA Minimum vs. Recommended
Scenario
Min (gal/person/day)
Min (L/person/day)
Guidance
Grab-and-go kit
1 gal
3.8 L
At least 3 days (CDC)
Home hurricane supply
1 gal
3.8 L
2-week supply if possible (CDC)
Very hot weather
up to 2 gal
up to 7.6 L
Needs can double (Ready.gov)
Children, nursing mothers, sick people
1 gal+
3.8 L+
May need more (Ready.gov)
Pet per animal
by weight
0.2–1.1 L
Cat ~0.2 L, large dog ~1.1 L (vet formula)
Critical: These figures are for water storage only. Don't count on pool water for drinking, and don't use water heater water if the tank or home has flooded. Always have safe drinking water in sealed containers.
🌀 When to Use This
Who Needs a Hurricane Water Prep Calculator
Hurricane Season Preparation (June–November)
Coastal and inland residents in the Gulf Coast, Atlantic seaboard, and Caribbean should calculate and store water before the season peaks in August and September. Once a storm watch is issued, bottled water can sell out quickly, so buy and fill containers early.
Tropical Storm and Flash Flood Zones
Even tropical storms below hurricane strength can disrupt water systems for days through power cuts, pipe breaks or boil-water notices. This calculator helps you prepare for those scenarios too.
Off-Grid and Rural Households
Homes on well pumps lose water immediately when power fails. If your well relies on an electric pump, your effective water supply is zero the moment the grid goes down — making pre-stored water non-negotiable.
Apartment and Condo Dwellers
Many taller buildings rely on electric booster pumps to get water to upper floors, so taps can run dry in a power cut even when the city supply is still working. Ask your building manager how your water is supplied.
Households with Medical Dependencies
People on home dialysis, with wound care needs or with weakened immune systems may need more safe water than the 1-gallon minimum. Enter the extra amount in the medical field, and follow the emergency plan from their care team.
🧮 Worked Example
Worked example: a 2-week hurricane supply for a family of four
Two adults, two children and a medium dog (~20 kg), hot and humid weather (×1.5), moderate activity (×1.15), 14 days:
Factor: 1.5 × 1.15 = 1.725, so each person gets 3.785 × 1.725 = 6.53 L a day.
People: 4 × 6.53 = 26.1 L a day. Dog: 0.67 × 1.725 = 1.16 L a day.
Total: 27.27 L × 14 days = 382 L — about 101 US gallons, or 21 × 5-gallon jugs (the last part-full). It weighs about 382 kg (842 lb), so store it at ground level.
At the bare minimum (mild weather, sheltering) the same family would need 221 L for 2 weeks; for a 3-day grab-and-go kit in the hot-weather setting, about 82 L.
❓ FAQ
Frequently Asked Questions
How much water should I store for a hurricane?
The Ready.gov and CDC baseline is 1 gallon (3.8 L) per person per day for at least 3 days, and the CDC suggests a 2-week supply at home if possible. Because hurricanes come in hot weather — often with no power for air conditioning — this calculator adds heat and activity factors on top, since needs can double in very hot temperatures.
Is 1 gallon per person per day really enough during a hurricane?
It's a minimum, not a comfort level. If about 3 litres a day go on drinking and food — the top of the Sphere humanitarian survival range — less than a litre is left for washing and sanitation. In heat, and with cleanup work, needs rise sharply; Ready.gov notes they can double. With the default hot/humid and moderate settings, this calculator uses about 1.7 gallons (6.5 L) per person per day.
How long does stored water stay safe to drink?
Follow the expiration date on store-bought water. Water you bottle yourself should be replaced every 6 months (CDC), and kept somewhere cool — the CDC suggests 50–70 °F (10–21 °C) — and dark, away from fuel and pesticides. Treated tap water needs no additives; bleach is for disinfecting water that may be unsafe, not for extending storage. Don't use milk or juice jugs, which are hard to clean properly.
Can I use my swimming pool or hot water heater as emergency water?
Pool water is not for drinking: it contains pool chemicals and can be contaminated by people, animals and storm debris — use it for flushing toilets and cleaning. The water in your water heater can be used in an emergency if the tank and your home have not flooded: turn off the power or gas first, let it cool, and drain it from the valve at the bottom. If you're unsure whether it is safe, treat it before drinking. Stored sealed containers remain the most reliable option.
What containers are best for storing emergency water?
Use food-grade containers such as HDPE (recycling code #2) water jugs. Practical options include commercial 5-gallon water jugs, stackable 5–7 gallon jugs, bathtub storage liners filled just before the storm, and 55-gallon food-grade drums with a pump. Clean and sanitise containers first (CDC: 1 teaspoon of unscented bleach per quart of water), never reuse containers that held chemicals, and store water away from fuel, pesticides and direct sun.
How much water does a nursing mother or pregnant woman need?
The US National Academies' adequate intake for total water (from drinks and food) is about 3.0 L a day during pregnancy and 3.8 L a day while breastfeeding, against 2.7 L for other adult women. Count these individuals as adults and add about 1 L a day for each of them in the medical field. If you use powdered infant formula, store enough safe water to make it up.
What is a good hurricane water prep plan for a family of 4?
For 2 adults and 2 children in hot, humid weather with moderate activity, a 7-day outage needs about 183 litres (48 US gallons) — about 10 five-gallon jugs. For the CDC's suggested 2 weeks, it is about 366 litres (97 gallons), or 382 litres with a medium dog, as in the worked example. Store it in a cool, dark area, and keep a way to treat water — such as unscented bleach or purification tablets — as a backup. This calculator provides the exact figure based on your specific household inputs.
Should I store water before or after a hurricane warning is issued?
Always before — ideally well before hurricane season begins in June. Once a hurricane watch or warning is issued for your area, water, batteries and fuel can sell out quickly. Calculate your needs now using this tool, purchase your storage containers and water supply, and rotate it every 6 months so you're always prepared when a storm approaches.
✅ Sources & Review
Sources and review
The base rate and durations are official preparedness guidance; the in-between heat and activity factors are our planning steps and are labelled as such.
Ready.gov (FEMA) — Water: at least 1 gallon per person per day; 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.
