Water Storage Tanks for Emergencies: How to Size One and Where to Put It

Water storage tanks are the step up from a closet full of stacked jugs. Once the last shelf is full and you still are not comfortable, the next move is one big vessel instead of thirty small ones. Good instinct. It is also where most people make their only expensive mistake, because a tank decision is mostly physics and siting, not brand.

The tank is the easy part. The floor under it and the way you get water back out of it are the hard parts. So let's go in order: how many gallons, what that weighs, where it can safely sit, what it should be made of, and how you get a drink out of it with the power off.

What size water storage tank do you actually need?

Start at 2 gallons per person per day, then multiply by the number of days you want to cover.

The CDC says to store at least 1 gallon of water per person, per day for 3 days, and to aim for a 2 week supply if you can. That 1 gallon is the drinking and cooking floor. Utah State University Extension adds one half to 1 gallon per person per day on top of that for personal hygiene and dishwashing. Add them and 2 gallons per person per day is a realistic planning figure.

For a family of 4, that is 8 gallons a day, 56 gallons for a week, 112 gallons for 2 weeks, and 240 gallons for a month.

Now the part that resets expectations. Penn State Extension notes that a person in the United States uses 80 to 100 gallons per day at home. A 320 gallon tank, which looks enormous in a garage, holds about one normal day for a family of 4. The tank is not replacing the utility. It is buying time at a much lower rate of use.

What do flushing and washing actually cost you?

More than your whole tank, which is why you plan for them separately. Penn State Extension puts a low flush toilet at 1.6 gallons per flush, an older toilet at 5 gallons, and one 8 minute shower at 20 gallons.

Four people flushing a low flush toilet 4 times a day is about 25.6 gallons daily, or roughly 358 gallons over 2 weeks. That is more than a 320 gallon slimline holds, and with 5 gallon toilets it is over 1,100 gallons. Four daily showers for 2 weeks is 1,120 gallons.

You are not storing potable water for any of that. Flush water comes from a rain barrel, a pool, a creek, or a bathtub you filled before the storm. Your clean tank is for drinking, cooking, teeth, and a washcloth bath. Keeping those two streams separate is what makes a 160 gallon tank feel generous instead of pointless.

How much does a full water storage tank weigh?

Multiply gallons by 8.33 and you have pounds. The USGS Water Science School puts 1 gallon of water at 70 degrees Fahrenheit at 8.329 pounds.

That gives numbers that surprise almost everyone:

• A 55 gallon drum holds 458 pounds of water.

• A 275 gallon IBC tote holds 2,291 pounds, more than a ton.

• A 550 gallon vertical tank holds 4,581 pounds.

Weight is only half of it. What matters structurally is how concentrated it is. A standard IBC tote sits on a pallet footprint of about 40 by 48 inches, roughly 13 square feet. Divide 2,291 pounds by 13 and about 172 pounds is pressing on every square foot of that one patch of floor.

Residential floors are designed for people and furniture spread across a room, not a ton of water parked in one spot. If you are considering an upstairs room, a basement joist bay, or a crawlspace deck, that is a question for your building department or a structural engineer, not a forum thread. One phone call, and it is the cheapest part of the project.

Where should you put a water storage tank?

On a garage slab or a ground level pad, against a wall, out of the sun. That is the default answer and it is right most of the time.

A concrete slab sits on compacted earth and carries a concentrated load without complaint. A wood framed floor does not, and a crawlspace deck really does not. The same tote that is a non issue in a garage is a serious question in a finished bonus room. A few rules worth following:

• Level and fully supported. A large plastic tank needs continuous support under its whole base. Blocking up the corners and leaving the middle unsupported is how you crack one.

• Out of direct sun. The CDC says keep containers away from direct sunlight and store water at 50 to 70 degrees Fahrenheit. Sun also degrades plastic over years.

• Off the bare ground. Utah State University Extension recommends a clean, dry place off the ground, away from gasoline, kerosene, and pesticides, whose vapors can move through plastic.

• Anchored if wind or flood is a risk. FEMA's guidance for drinking water systems is to anchor tanks to platforms with corrosion resistant straps so a tank cannot float loose, and to fill tanks before a storm to add weight.

An empty tank is cheap to move. A full one is furniture. Decide where it lives before you fill it the first time.

What are water storage tanks made of, and does it matter?

It matters, and the only thing you have to confirm is that the tank is sold as food grade for potable water.

Most home tanks are high density polyethylene, the plastic stamped with a 2 in the recycling triangle. That resin code alone does not make a container food safe. It only names the plastic family. The CDC says to use FDA approved food grade water storage containers, and Utah State University Extension is direct that non food grade plastics are not recommended, along with pewter and lead soldered metals. If a listing will not say food grade or potable, keep shopping. More detail is in our guide to food grade water storage containers and what the resin codes actually mean.

Then pick opaque over translucent, every time. Algae needs light to grow, so a translucent tank in a bright garage becomes a slow green science experiment. A dark, opaque tank denies algae the one input it cannot do without, and it matches the CDC's instruction to keep stored water out of direct sunlight. You give up eyeballing the level, and a dipstick solves that.

Are IBC totes safe for drinking water?

Only if you can confirm what was in it before, and with a used tote you usually cannot.

Used totes are cheap, hold 275 or 330 gallons, and stack. They are also the most common secondhand industrial container in the country, and they have carried everything from food syrup to solvents to farm chemicals. The CDC says plainly not to use containers that previously held toxic chemicals, and the EPA's emergency disinfection guidance rests on the same logic: bleach and boiling handle germs, not chemistry. You cannot chlorinate solvent residue out of a tank wall.

So buy new and labeled food grade, or buy used with a prior contents label you can verify. If the only honest answer to "what was in this" is "the guy said water," use it for flush and garden water and buy a new tank for drinking.

How do you protect a water storage tank from freezing?

Leave room for expansion and keep the tank where it will not freeze solid. The USGS notes that the density of ice is about 9 percent lower than liquid water, so freezing water takes up more room than it did. In a rigid tank filled to the brim, that expansion goes into the walls, the fittings, and the valve, which is why a cracked spigot is the classic cold climate failure.

• Leave headspace in freezing conditions instead of topping off to the brim.

• Site the tank in a garage or conditioned space, not against an outdoor north wall.

• Drain the spigot and any exposed line after each use. A cup of water in a fitting freezes long before a ton of water in a tank does.

• A large mass of water freezes slowly. A full 320 gallon tank in an unheated garage rides out a cold night better than a row of jugs.

One honest conflict worth naming. The CDC advises filling a cistern to maximum capacity before a disaster, and FEMA says to fill tanks before a storm for weight. That is wind and flood advice, and it is good. In a hard freeze, headspace wins. Read the hazard in front of you.

How do you get water out of a tank without power?

Gravity, a siphon, or a hand pump. Pick one before you buy, because a sealed tank with a top fitting and no plan is a very heavy decoration.

Gravity is simplest, and it has one requirement: the outlet has to sit higher than whatever you are filling. A spigot 4 inches off a slab will not fill a 5 gallon bucket. Set the tank on a sturdy platform, or run a short hose from a bottom fitting into a bucket below it. Three setups that work:

1. Bottom bulkhead fitting and a ball valve. Best flow, and you can attach a hose. Shield the valve from bumps and freezing.

2. Siphon hose. Cheap, works on drums with only a top bung, and needs nothing but a hose and a squeeze bulb. Keep a dedicated potable hose.

3. Manual drum pump. Screws into a drum bung and lifts water from the top. Slow but foolproof, and it does not care how tall the tank is.

Test the whole chain once, with water in the tank, on a normal Saturday. Fill a bucket and time it. That 10 minute test is the difference between a plan and a purchase.

How often should you rotate and sanitize a water storage tank?

Treat water you bottled yourself as a 6 month item, and sanitize the tank whenever you empty it.

The CDC says replace water every 6 months if you fill the containers yourself, and Utah State University Extension says check it every 6 to 12 months. To sanitize an empty container, the CDC's recipe is 1 teaspoon of unscented liquid household chlorine bleach containing 5 to 9 percent sodium hypochlorite in 1 quart (4 cups) of water, swirled through, held at least 30 seconds, poured out, and air dried. Utah State University Extension gives it as 1 tablespoon per gallon.

For a large tank you disinfect in place, the CDC's cistern safety guidance gives amounts by tank size, using 5 to 9 percent bleach:

The process: add the bleach, run faucets until you smell chlorine, let it sit at least 12 hours, drain, refill, and run the faucets until the smell is gone. For scrubbing a tank interior the CDC gives 1 cup of bleach in 10 gallons of water. For shelf life, see our breakdown of how long stored water stays safe to drink.

What most guides skip about water storage tanks

Two things, and they are the two that decide whether the tank works.

The first is the floor. Nearly every guide helps you pick gallons and skips the surface underneath. But the floor is the only part of this project that can fail catastrophically, and the only part you cannot fix once the tank is full. Check it first. Garage slab, ground level pad, or a conversation with someone qualified. There is no fourth option.

The second is the exit. A tank you cannot get water out of without power is a tank you do not really have. Plenty of people plumb a tote into a small electric pump and never test it on a dead circuit. Gravity, a siphon, and a hand pump all work without a grid, and one of them should be sitting next to the tank right now.

One honest note: a big tank is not automatically better than jugs. Jugs are portable and they fail one at a time. A tank is efficient and stationary. Most households are happiest with both, which is why it is worth revisiting how much water to store per person before you size anything. You don't have to be extreme to be ready.

Frequently asked questions

How many gallons should a family of 4 store in a water tank?

About 112 gallons covers 2 weeks at 2 gallons per person per day. The CDC's floor is 1 gallon per person per day for drinking and cooking, and Utah State University Extension adds a half gallon to 1 gallon for hygiene. A 160 gallon tank covers that with margin.

How much does a 275 gallon IBC tote weigh when full?

About 2,291 pounds of water, plus the tote and cage, using the USGS figure of 8.329 pounds per gallon at 70 degrees Fahrenheit. Over a standard 40 by 48 inch pallet footprint that is roughly 172 pounds per square foot, which is why a full tote belongs on a concrete slab.

Can I keep a water storage tank in my basement?

Only if it sits directly on the basement slab and you can get water out without power. A tank on a poured floor is fine structurally. On a raised platform, a joist bay, or a crawlspace deck, it is a question for your building department. Plan the exit too, since a basement tank means carrying buckets upstairs.

Do water storage tanks need to be opaque?

Opaque is strongly preferred, because algae needs light to grow and a dark tank denies it. It also fits the CDC's instruction to keep stored water away from direct sunlight and at 50 to 70 degrees Fahrenheit. Use a dipstick or a sight tube to check the level.

Is a used IBC tote safe for drinking water?

Not unless you can verify what it held before. The CDC says not to use containers that previously held toxic chemicals, and the EPA is clear that fuel and toxic chemicals cannot be treated out of water. Bleach and boiling kill germs, not chemistry. Save unverified used totes for flush and garden water.

The numbers, in one place

Weights use 8.329 pounds per gallon (USGS, at 70 degrees Fahrenheit). Days assume a household of 4 at 2 gallons per person per day, combining the CDC drinking minimum with the Utah State University Extension hygiene allowance.

Start with the pad, not the price tag

Make it an order of operations. Find the flat, shaded, ground level spot first and measure it. Size the tank to fit that spot and your real daily use. Then work out how water gets into a bucket with the power off. The gallons are the last decision, not the first. One 55 gallon drum on a garage slab, filled, dated, and fitted with a siphon hose, is 6 days of water for a family of 4. Start with what you have. Build from there.

You never know, but you can always be ready.

Sources: CDC, How to Create and Store an Emergency Water Supply, CDC, Cistern Safety and Disasters, EPA, Emergency Disinfection of Drinking Water, Utah State University Extension, Water: Storage and Emergency Use, Penn State Extension, Water System Planning: Estimating Water Needs, USGS Water Science School, Water Density, FEMA P-2181 Fact Sheet 4.1, Drinking Water Systems.