How Much Water to Store Per Person: Daily Needs, Pets, and How to Size Your Supply

Key points

• Store at least 1 gallon of water per person per day. That gallon covers drinking and sanitation together, not drinking alone.

• Three days is the floor. Two weeks is the target the CDC actually asks you to reach if you can.

• A family of 4 with a 50 pound dog needs about 14 gallons for 3 days and about 63 gallons for 2 weeks.

• Water weighs 8.34 pounds per gallon. That 2-week supply is 525 pounds, and a full 55 gallon drum (459 pounds of water) is not something you can move.

• Keep flush and wash water separate and cheap. Toilets alone would eat 32 gallons a day for a family of 4, which nobody stores in jugs.

Almost everyone knows how much water to store per person: 1 gallon, per person, per day. Almost nobody does the second half of the arithmetic, which is what that quantity weighs, where it sits, and how fast it disappears when it is also doing the dishes.

A case of bottled water is 3.17 gallons. For a family of 4, that is 19 hours. The three cases in your garage that feel like a supply are 2 and a half days.

Here is the whole calculation, including the part that decides whether your plan survives contact with your actual floor.

How much water should you store per person per day?

At least 1 gallon per person per day. That is the number both FEMA and the CDC use, and they use it for a reason: it is the point below which normal household function starts breaking down.

Ready.gov, FEMA's preparedness site, puts it as at least one gallon of water per person per day for several days, for drinking and sanitation. The CDC's guidance is 1 gallon of water per person, per day for 3 days, with a 2-week supply if you can manage it.

One gallon is 128 ounces. A person drinking normally goes through 64 to 100 ounces of it. What is left over, roughly a quart, is doing everything else.

Does 1 gallon per person per day include sanitation?

Yes, and this is the single most misread number in preparedness. The gallon is not a drinking allowance. The CDC spells out that the 1 gallon covers drinking, cooking, brushing teeth, and other uses. Ready.gov says the same thing in four words: for drinking and sanitation.

Run through a real day and it goes fast:

• Drinking: 64 to 100 ounces

• Cooking and rehydrating food: 8 to 24 ounces

• Brushing teeth, twice: 4 to 8 ounces

• Washing hands and face, a few times: 8 to 16 ounces

• Rinsing dishes and utensils: whatever is left, and it will not be enough

People who plan a "drinking only" stash discover on day 1 that the pot they cooked in needs rinsing, and the gallon they set aside for tomorrow's drinking is now dishwater. Plan the gallon as a whole-day budget and it holds. Plan it as a drinking budget and you are short by half within 24 hours.

What the gallon does not cover at all is flushing. That gets its own supply, further down.

Who needs more than 1 gallon a day?

More people than you would think, and the adjustments are additive.

• Hot weather. Ready.gov is blunt: in very hot temperatures, water needs can double. Plan 2 gallons per person per day for a summer outage in the South or Southwest, especially with no air conditioning.

• Children, nursing mothers, and people who are sick. Ready.gov names all three as needing more. Anyone with vomiting or diarrhea is losing fluid faster than they are taking it in, and that is exactly the illness pattern a water emergency produces.

• Pregnancy. The CDC specifically calls out storing more water for pregnant women.

• Altitude. This one is invisible until it bites. The National Academies volume on nutrition at high altitude, hosted by NIH, notes that intake is reduced at high altitudes whenever fluids are allowed ad libitum because of a decrease in the sensation of thirst, and that reduced intake alone can account for roughly 2 to 3 liters of negative fluid balance during the first few days at altitude, on top of an increase in insensible loss from low humidity and hyperventilation. If you live or shelter high up, add water and drink on a schedule rather than waiting to feel thirsty.

• A medical emergency in the house. Ready.gov flags this too. Wound irrigation, a colostomy, dialysis supplies, or a family member on a fluid protocol all raise the number.

One rule survives all of these: Ready.gov's instruction to never ration drinking water unless authorities tell you to. Drink what you need today and work the problem of getting more tomorrow. Dehydrated people make bad decisions, and bad decisions are what actually hurt people in an outage.

Should you store a 3-day supply or a 2-week supply?

Store 3 days if that is all you can manage today, then keep going to 2 weeks. Two weeks is the more useful target, and both agencies point at it.

The CDC's page frames 3 days as the baseline and asks you to try for a 2-week supply if possible. Utah State University Extension is more direct, recommending a minimum of a three-day supply of water per person, but it would be best to have a two-week supply in your home for each family member.

The reason to prefer 2 weeks is not that disasters are longer than they used to be. It is that 3 days assumes outside help arrives on schedule. In a regional event, the utility crews, the bottled water trucks, and the road crews are all working the same backlog you are in. Three days covers a bad thunderstorm. Two weeks covers a hurricane, a hard freeze that bursts mains across a metro area, or a treatment plant that goes offline while a part gets shipped.

The honest math is also friendlier than it sounds. Going from 3 days to 2 weeks for a family of 4 is 12 gallons to 56 gallons. That is one 55 gallon drum, or eleven 5 gallon jugs, or about 18 cases of bottled water. It is a weekend project and a couple hundred dollars, not a renovation.

How much water do pets need per day in an emergency?

Plan about 1 ounce of water per pound of body weight per day, then round up.

That number comes from a real clinical figure. The Merck Veterinary Manual states that in a thermoneutral environment, most mammalian species need about 44 to 66 mL/kg body weight per day. The top of that range works out to almost exactly 1 fluid ounce per pound, which makes it easy to do in your head.

Worked out by size, at the top of the range:

• 10 pound cat: about 10 ounces a day, roughly 0.08 gallons. Call it half a gallon a week.

• 25 pound dog: about 25 ounces a day, roughly 0.2 gallons.

• 50 pound dog: about 50 ounces a day, roughly 0.4 gallons.

• 80 pound dog: about 80 ounces a day, roughly 0.6 gallons.

Then add a margin. Animals in a hot house without air conditioning drink more, stressed animals drink more, and you will spill some and rinse the bowl. For planning, round a 50 pound dog to half a gallon a day and a cat to a tenth of a gallon a day. If you are building the rest of the animal's kit at the same time, our pet emergency kit checklist covers the paperwork and carrier problems that decide whether a shelter takes your animal at all.

What does a family of 4 with a dog actually need?

Here is the whole thing worked out, in gallons, in containers, in floor space, and in pounds. The household is 2 adults, 2 children, and a 50 pound dog.

Three days

• People: 4 x 1 gallon x 3 days = 12 gallons

• Dog: 0.5 gallons x 3 days = 1.5 gallons

• Total: about 14 gallons

• Weight: 117 pounds

• What it looks like: three 5 gallon jugs (15 gallons, 125 pounds), or 5 cases of 24 half-liter bottles (15.9 gallons). Three jugs side by side occupy about 11 inches by 33 inches, roughly 2.5 square feet of floor, and stand about 20 inches tall.

That is a closet corner. Anyone can do this today.

Two weeks

• People: 4 x 1 gallon x 14 days = 56 gallons

• Dog: 0.5 gallons x 14 days = 7 gallons

• Total: about 63 gallons

• Weight: 525 pounds

• What it looks like: thirteen 5 gallon jugs, or one 55 gallon drum plus two 5 gallon jugs, or about 20 cases of bottled water.

• Floor space: thirteen jugs in a single layer cover about 11 square feet, roughly a 3 foot by 4 foot patch. Stacked 2 high on a rack, about 5 or 6 square feet. Twenty cases stacked 4 high take about 6 square feet.

525 pounds is the number that reframes the project. It is a piano, sitting in your utility room. That is not a reason to skip it. It is a reason to decide where it goes before you buy it.

How much does stored water weigh, and will your floor hold it?

Water weighs 8.34 pounds per gallon, and this is the part most water storage guides never mention.

The USGS puts the density of water at about 62.4 pounds per cubic foot. A cubic foot is 7.48 gallons, so a gallon comes to 8.34 pounds. Every container you fill obeys that:

• 1 gallon jug: 8.3 pounds

• Case of 24 half-liter bottles: 3.17 gallons, about 26 pounds

• 5 gallon jug: 42 pounds, which is the practical ceiling for most people to carry with one hand

• 7 gallon container: 58 pounds

• 55 gallon drum: 459 pounds of water, about 480 pounds with the drum

The floor-loading reality

A 55 gallon drum is about 23 inches across, which is a footprint of roughly 2.9 square feet. Put 480 pounds on 2.9 square feet and you are applying about 165 pounds per square foot.

Now compare that to what a house is built for. HUD's residential structural design guide lists the design live loads used for wood-framed homes: 40 pounds per square foot for living areas and 30 pounds per square foot for bedroom areas. Attics with storage are rated at 20.

To be fair about it, those are uniform design loads, floors carry safety factors, and a drum's weight spreads through the subfloor into several joists rather than sitting on one point. A full drum on a wood floor is not going to drop through the ceiling tomorrow. But it is roughly 4 times the area load the floor was designed around, sustained indefinitely, and that is a bet worth not taking. Practical placement rules:

• Barrels and drums belong on a concrete slab. Basement floor, garage floor, ground-level utility room.

• If a large container has to sit on a framed floor, put it directly over a bearing wall or a main beam, and orient any rack so the load crosses as many joists as possible.

• Spread the weight. Twelve 5 gallon jugs in one layer put about 50 pounds per square foot on the floor. The same 60 gallons in a single drum puts 165.

• Do not store water in large containers on a second floor or in an attic.

The other thing nobody mentions: a full drum does not move

A 55 gallon drum full of water cannot be lifted, cannot be carried, and cannot safely be tipped or rolled by one person. Once you fill it, it lives where you filled it until you empty it. That means two things. Fill it in its final location, using a hose, and put a bottom spigot on it or keep a siphon pump with it, because you will not be pouring anything out of the top.

This is also the argument for a mixed setup rather than one big container. Drums are the cheapest way to hold a lot of water. Jugs are the only way to move it to where a person is. Most households do best with one large container for volume and half a dozen 5 gallon jugs and a few 1 gallon bottles for actual daily use.

How do you store flush and wash water cheaply?

You store it in whatever holds water, because the volume you need for sanitation is far beyond what anyone keeps in food-grade containers.

Do the flushing math. The current federal standard for toilets is 1.6 gallons per flush, per the EPA, with WaterSense-labeled models at 1.28 and pre-1994 toilets using as much as 6 gallons. The EPA notes toilets are nearly 30 percent of an average home's indoor water use. A family of 4 flushing 5 times each per day is 20 flushes, which at 1.6 gallons is 32 gallons a day. Your entire 2-week drinking supply would be gone in 2 days of normal flushing.

So split the supply in two and spend almost nothing on the second half:

• Fill the bathtub before the storm. A standard tub holds 40 to 60 gallons. A cheap bathtub bladder liner keeps it clean and stops the slow drain leak that empties a plain tub overnight. This is the highest-volume, lowest-cost move available to you, and it takes 5 minutes.

• Clean lidded trash cans with food-grade liners. A 32 gallon can is a few dollars and holds a day of flushing.

• A rain barrel off a downspout. 50 to 60 gallons that refills itself. Not drinking water, ever, without treatment. Roof runoff carries whatever is on your roof.

• 5 gallon buckets with lids. Stackable, cheap, and the right size to actually carry.

• Water you already have. A typical water heater holds 40 to 50 gallons, and there is a gallon or two in each toilet tank (the tank, not the bowl). Know where the heater's drain valve is before you need it, and shut off the supply first so you are not drawing contaminated water into your clean containers.

To flush without a working supply, pour about 1.5 to 2 gallons quickly straight into the bowl. The bowl siphons on its own. You do not need to fill the tank.

Two hard rules on the non-potable side. Never drink from the tub, a rain barrel, a pool, or a water heater without treating it first, and label the non-potable containers clearly so a tired person at 2 a.m. does not grab the wrong one. If you need to make some of it drinkable, the boil and bleach numbers are in our guide to what to do during a boil water advisory.

How often should you rotate stored water?

Every 6 months for water you bottled yourself, and by the printed date for water you bought.

The CDC's instruction is to replace self-filled containers every 6 months and to observe the product date on store-bought bottled water. Ready.gov says water that has not been commercially bottled should be replaced every 6 months. Utah State Extension recommends rotating every 6 months for quality even though properly disinfected and sealed water technically has an indefinite shelf life.

Storage conditions matter more than the calendar. The CDC's target is 50 to 70 degrees F, out of direct sunlight, and away from gasoline, pesticides, and solvents, because vapors can move through plastic over time. A jug that spent the summer on a sunny garage shelf is in worse shape at 3 months than a jug in a basement is at a year. If you want the longer version of what actually degrades and what does not, we covered it in how long you can store water safely, and the container materials question in which water storage containers are actually food grade.

The practical trick is to hang rotation on something you already do. Twice a year, at the daylight saving time changes, dump the stored water on the garden and refill. It takes 20 minutes and you never have to remember a date.

Why most people store far less than they think

Because a case of bottled water looks like a lot and is not.

A 24-pack of 16.9 ounce bottles is 405.6 ounces, which is 3.17 gallons. Run that against 1 gallon per person per day:

• 1 case = 3 days for 1 person, or 19 hours for a family of 4

• 3 cases = 9.5 gallons = 2.4 days for a family of 4

• A 2-week supply for that family = about 20 cases

Almost nobody has 20 cases in the garage. Most people have 2 or 3 and a vague sense that they are covered. That gap between the felt supply and the counted supply is the whole problem, and it closes the moment you write the number on a piece of tape and stick it to the shelf.

Two other quiet shortfalls worth checking. First, half-empty containers. A jug that has been sipped from is not a stored gallon, it is a half gallon and an open container. Second, flimsy single-use jugs, the thin translucent gallon milk-style jugs from the grocery store. Those are designed for a few weeks on a shelf, not a year in a garage, and they split at the seams. If a container is bowing, sweating, or crackling when you squeeze it, it is not part of your supply anymore.

Honest limits and when to get help

Storage is a bridge, not a solution. A 2-week supply buys you time to find more water, not permission to stop thinking about it. Pair the storage with at least one way to treat water you find, whether that is a stove and fuel, unscented bleach, or a filter rated for parasites.

Watch for dehydration rather than assuming everyone is drinking. The signs are dark or very little urine, dizziness on standing, dry mouth, headache, and unusual sleepiness or irritability, and they show up earlier in small children and older adults. Call a doctor if someone cannot keep fluids down, has not urinated in 8 hours, or is confused. Call 911 for fainting, a seizure, or unresponsiveness.

Call Poison Control at 1-800-222-1222 if someone drinks from a container that previously held anything but food or water, or if stored water tastes or smells of chemicals or fuel. That last one is not paranoia. It is the most common way a garage water supply goes bad.

Frequently asked questions

How much water should I store per person?

At least 1 gallon per person per day, covering drinking and sanitation together, for a minimum of 3 days and ideally 2 weeks. That is 3 gallons per person for the short plan and 14 gallons per person for the 2-week plan. Add more for hot climates, children, pregnancy, illness, and altitude.

Is 1 gallon per person per day enough?

It is the minimum, not a comfortable amount. The gallon has to cover drinking, cooking, brushing teeth, and washing, and it does not cover flushing at all. In very hot weather Ready.gov says water needs can double, so plan 2 gallons per person per day for a summer outage.

How much water do I need for 2 weeks for a family of 4?

About 56 gallons for the people, plus roughly 7 gallons for a 50 pound dog, so call it 63 gallons. That weighs about 525 pounds and takes up 11 square feet of floor as thirteen 5 gallon jugs in one layer, or about 6 square feet stacked.

How much water does a dog need per day in an emergency?

Plan about 1 ounce per pound of body weight per day, which comes from the Merck Veterinary Manual figure of 44 to 66 mL per kg. A 50 pound dog needs roughly 50 ounces, about 0.4 gallons. Round up to half a gallon a day to cover heat, stress, and rinsing the bowl.

How much does a 55 gallon water drum weigh when full?

About 459 pounds of water, or roughly 480 pounds including the drum, since water weighs 8.34 pounds per gallon. On its 2.9 square foot footprint that is about 165 pounds per square foot, well above the 40 pounds per square foot design live load HUD lists for residential living areas. Put drums on a concrete slab, and fill them where they will stay.

How often should I rotate stored water?

Every 6 months for water you filled yourself, and by the printed date for commercially bottled water. Store it at 50 to 70 degrees F, out of sunlight, and away from gasoline and pesticides. Tying the swap to the twice-yearly clock change is the easiest way to remember.

You never know, but you can always be ready.

Sources: Ready.gov (FEMA), Water | Ready.gov (FEMA), Build A Kit | CDC, How to Create and Store an Emergency Water Supply | Utah State University Extension, Storing Water for an Emergency | USGS Water Science School, Water Density | Merck Veterinary Manual, Nutritional Requirements of Small Animals | HUD, Residential Structural Design Guide, Design Loads for Residential Buildings | EPA WaterSense, Residential Toilets | National Academies (via NIH), Fluid Metabolism at High Altitudes