Enter your household size, emergency duration, and activity level — get the exact water volume you need to store, in litres, gallons, and number of containers.
Fill in your household details and get the exact volume to store
Household & Scenario
Adults
Children
Pets (dogs/cats)
Duration (days)
Activity Level & Scenario
Usage Level
Climate / Heat
Typical Pet Size
⚠ Please enter at least 1 person (adults or children) and a duration of at least 1 day.
Your Storage Requirement
Total Water to Store
—
Litres (L)
US Gallons
— gal
UK Gallons
— gal
Per Person/Day
— L/day
× 1L Bottles
— bottles
× 5L Containers
— units
× 20L Jerry Cans
— cans
Weight (full)
— kg
Weight (lbs)
— lbs
Official MinimumMeets the Ready.gov / CDC minimum of 1 gallon per person per day.
Storage Breakdown by Person-Days
📖 How To Use
How to Use This Calculator
Getting your emergency water storage requirement takes less than 30 seconds:
Enter your household count
Put in the number of adults and children. Both are counted at the same rate, because official guidance doesn't reduce it for children — and children, nursing mothers and sick people may need more. Add your pets and pick a typical size: a cat needs about 0.2 L a day, a medium dog about 0.7 L and a large dog about 1.1 L, using the veterinary maintenance formula (30 mL × body weight in kg + 70 mL).
Set the emergency duration
The CDC's baseline is at least 3 days, and it suggests a 2-week supply at home if you can. Use 3 days for a grab-and-go kit and 14 days or more for home storage. Off-grid homes should size storage with the off-grid calculator instead.
Choose your usage level
"Drinking only" is 3 L a person a day — the top of the 2.5–3 L survival range in the Sphere humanitarian standards. "Official minimum" is the Ready.gov / CDC 1 gallon (3.8 L) for drinking and basic sanitation. "Comfortable" (2 gallons) adds cooking and washing; "Full use" (3 gallons) allows some washing of people and dishes.
Select your climate condition
Ready.gov notes that in very hot temperatures water needs can double. Leave it at "Normal" for mild weather, and choose a higher factor if your emergency is likely to happen in summer heat or without air conditioning.
Hit Calculate
You get total litres, gallons, weight, and the number of standard containers required. Copy or print the result and use it as your shopping list.
Critical reminder: Stored water must be rotated. For store-bought water, follow the date on the bottle. Water you bottle yourself should be replaced every 6 months (CDC). Use food-grade containers only — never ones that held chemicals, and not milk or fruit-juice jugs, whose residues are hard to remove.
📐 The Formula
Emergency Water Storage Formula
The calculation is straightforward once you know the per-person daily requirement:
Total Litres = ((Adults + Children) × Person_Rate + Pets × Pet_Rate) × Days × Climate_Factor
Person Rate (official minimum): 3.785 L/day (1 US gallon)
Pet Rate: (30 × body weight kg + 70) mL/day
Climate Multiplier: 1.0 – 2.0×
Daily Water Requirements by Use Case
Usage Level
L/Person/Day
Gal/Person/Day
Covers
Drinking Only
3 L
0.8 gal
Drinking and food (Sphere survival range 2.5–3 L)
Official Minimum
3.8 L
1.0 gal
Drinking + basic sanitation (Ready.gov, CDC)
Comfortable
7.6 L
2.0 gal
Drinking, cooking, basic hygiene
Full Use
11.4 L
3.0 gal
Drinking, cooking, some washing of people and dishes
For comparison, the Sphere humanitarian standards put basic needs at 7.5–15 litres per person per day (2.5–3 L drinking and food, 2–6 L hygiene, 3–6 L cooking), and aim for at least 15 L in a relief setting. The 1-gallon household minimum assumes a short emergency at home with careful use.
Climate Adjustment Factor
Condition
Multiplier
Why
Normal / mild
× 1.0
The 1-gallon guidance as written
Warm
× 1.25
Warm weather or light physical work, more sweating
Hot summer
× 1.5
Hot weather without air conditioning, more risk of dehydration
Very hot / desert
× 2.0
Ready.gov: in very hot temperatures, water needs can double
The heat factor is applied to the whole daily amount as a simple, cautious allowance. Sweat losses depend on temperature, humidity and how active people are, so treat these factors as planning steps, not precise physiology.
🎯 Use Cases
When to Use This Calculator
🌀
Hurricane & Flood Prep
Storms and floods can cut power to pumps and contaminate supplies, leading to outages or boil-water notices. In hurricane-prone areas, aim for the CDC's 2-week home supply.
⚡
Extended 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. Three days is the minimum; longer outages are common after major storms.
🏕️
Off-Grid & Cabin Living
Calculate tank sizes for cabins, campsites, and remote properties where mains water isn't available. Pair with the rainwater harvesting calculators for a full system design.
🏚️
Bug-Out Planning
Determine how much water you can realistically carry versus how much you need to cache. Water is the heaviest supply item at 1 kg per litre — every litre counts.
🌏
Earthquake Zones
Earthquakes can break water mains and leave whole areas without safe tap water while repairs are made. In active seismic zones, keep at least the 2-week home supply and secure containers so they can't fall.
💧
Boil-Water Advisories
Boil-water notices can last from a day to several weeks. Stored safe water means you can drink and cook without boiling every litre, and still have water if power or fuel for boiling runs short.
Storage tip: Distribute storage across multiple container sizes. Large tanks hold bulk supply but are immovable. Keep at least a 3-day supply in portable jerry cans or bottles that can be taken with you if evacuation is needed.
🧮 Worked Example
Worked example: a 2-week home supply for a family of four and a dog
Two adults, two children and a medium dog (about 20 kg), at the official minimum of 1 gallon per person per day, for 14 days in normal weather:
People: 4 × 3.785 L = 15.14 L a day.
Dog: 30 × 20 + 70 = 670 mL, so 0.67 L a day.
Total: (15.14 + 0.67) × 14 days = 221 L — about 58.5 US gallons, or 12 × 20 L jerry cans (the last one part-full).
Weight: about 221 kg (488 lb) of water, so spread it across floor-level storage.
If the same emergency happens in a hot summer without air conditioning (×1.5), the total rises to about 332 L. A 3-day grab-and-go kit for the same family is about 47 L in normal weather.
❓ FAQ
Frequently Asked Questions
How much water should I store per person for an emergency?
Ready.gov (FEMA) and the CDC recommend at least 1 gallon (3.8 litres) per person per day for drinking and basic sanitation. That is a minimum: if you can, plan for 2 gallons (7.6 litres) to allow for cooking and washing. Children, nursing mothers and sick people may need more, and in very hot weather needs can double.
How long should my emergency water supply last?
The CDC's baseline is at least 3 days, and it suggests storing a 2-week supply if possible. Three days suits a grab-and-go evacuation kit; at home, large storms, earthquakes and long power cuts can disrupt water for longer, so 2 weeks is a sensible target where you have the space.
What containers are best for emergency water storage?
Use food-grade plastic (HDPE, marked with recycling symbol #2), stainless steel, or glass containers. Never reuse containers that held chemicals, and avoid milk or fruit-juice jugs — their residues are hard to remove and can let bacteria grow. Clean containers with dish soap and rinse, then sanitise them with 1 teaspoon of unscented household bleach in a quart (about 1 litre) of water, as the CDC describes. Store them somewhere cool and dark. The ideal mix is sealed commercial water bottles for portability, plus 20-litre jerry cans or a large tank for bulk storage.
How long does stored water stay safe to drink?
For store-bought bottled water, follow the expiration date on the bottle. Water you bottle yourself from a safe tap should be replaced every 6 months (CDC). Keep all stored water in a cool place — the CDC suggests 50–70 °F (10–21 °C) — away from sunlight and from fuels or pesticides. Bleach is for disinfecting water that may be unsafe, not for making stored water last longer; follow the CDC or your local health authority's dosing if you need to treat water.
How much water do pets need in an emergency?
A common veterinary estimate of daily maintenance fluid for dogs and cats of 2–70 kg is 30 mL × body weight in kg + 70 mL (MSD Veterinary Manual). That works out at about 0.2 L a day for a 4 kg cat, 0.7 L for a 20 kg dog and 1.1 L for a 35 kg dog. Pets need more in hot weather or when active, so the calculator applies the same heat factor to them. Ready.gov lists extra water for pets as part of your kit.
Is tap water safe to store for emergencies?
Yes — treated municipal tap water is safe to store. Fill clean, food-grade containers directly from the tap, seal tightly, label with the date, and store in a cool, dark location. Replace every 6 months. Water from a public supply is already treated, so no additives are needed — just replace it every 6 months. If your water comes from a private well, make sure it is safe to drink before you store it.
How heavy will my water storage be?
Water weighs about 1 kg per litre (8.34 lb per US gallon). A 72-hour supply for a family of 4 at the FEMA rate is about 45 litres — that's 45 kg (99 lbs) of water alone, not counting containers. For a 30-day supply, you're looking at 450+ kg. This weight must be distributed across storage locations and shelving rated for the load. Don't store large quantities on upper shelves.
What is the calculator for emergency water storage per person per day based on?
The main rate is the 1 gallon per person per day minimum from Ready.gov (FEMA) and the CDC, which covers drinking and basic sanitation. The drinking-only option uses the 2.5–3 L survival range from the Sphere humanitarian standards, and pet water uses the MSD Veterinary Manual maintenance formula. The heat factor follows Ready.gov's note that needs can double in very hot temperatures, with steps in between as a planning allowance.
✅ Sources & Review
Sources and review
This calculator follows official preparedness guidance. Where we add a step of our own — the in-between heat factors — the page says so.
Ready.gov (FEMA) — Water: at least 1 gallon per person per day; needs can double in very hot temperatures; replace water you bottle yourself every 6 months; don't ration drinking water unless told to.
Ready.gov — Build a Kit: one gallon per person per day for several days, plus extra water for pets.
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.
