How much water does a household need for three days, and where does it go?
Last updated October 16, 2026
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Last updated October 16, 2026
Plan on one gallon of water per person per day. A household of four needs about 12 gallons, or 45 liters, for three days. Roughly three quarters of each gallon is for drinking; the rest covers cooking, hand washing, teeth, and pets. Toilets can run on water you would never drink, so flushing does not come out of that number.
That is the whole answer for most households. The rest of this piece is about where those gallons actually go, where to find water you already own, how to store it in a small apartment without hating your closet, and how to make questionable water safe when the stored supply runs out.
The one-gallon rule, and what it covers
The federal guidance from Ready.gov is one gallon per person per day for drinking and sanitation. A normally active adult drinks about three quarters of a gallon of fluid a day, which leaves a quart for everything else. Children, nursing mothers, and anyone who is sick need more, and in very hot weather the need can double. If someone in the house takes medication that requires water or has a condition that calls for extra fluids, plan for them first.
One gallon is a floor, not a comfortable amount. It is the number at which nobody gets into trouble. Comfort starts a little above it.
Where 12 gallons goes in three days
Here is a day for a household of four, which is how we sized our own kit.
| Use | Per day, four people | Notes |
|---|---|---|
| Drinking | About 3 gallons | Three quarters of a gallon each; more in heat |
| Cooking and rehydrating food | Half a gallon to 1 gallon | Less if the pantry is ready-to-eat |
| Hand washing | Half a gallon to 1 gallon | A spray bottle or a jug with a spigot cuts this in half |
| Teeth, face, dishes | About a quart | Paper plates are a water-saving device |
| Pets | A quart or more | Dogs need roughly an ounce per pound of dog per day |
That lands at about four gallons a day, so a 12 gallon plan covers three days with a little margin, and the margin shrinks fast in July. Toilet flushing is not on the list because it should never come from drinking water. A modern toilet uses about 1.3 to 1.6 gallons per flush and an older one more than three, which is why the bathtub exists in the next section.
The water you already own
Before buying anything, count what is in the house.
The water heater. A tank-style water heater holds 40 to 50 gallons of clean water, which is more than most households would ever store on purpose. To use it: turn off the power or gas to the heater first, let it cool, open a hot tap somewhere in the house to let air in, and drain from the valve at the bottom of the tank into clean containers. If the municipal supply was contaminated before the outage, treat this water like any other questionable water.
Ice. The freezer ice is drinking water that doubles as food-safety insurance. Melt it when you need it, not before.
The bathtub. Fill it early, while there is pressure, and use it for flushing and washing. A bucket poured into the toilet bowl flushes it. Tub water is not for drinking unless it is treated, because tubs are not clean.
The toilet tank. The tank, not the bowl, holds a couple of gallons of the same water that comes out of the tap, assuming nobody has dropped a cleaning tablet in it. Treat before drinking.
Rain barrels and pools. Flushing and washing only. Pool water carries chemicals, and rain barrel water carries whatever was on the roof.
Storing 40 liters in an apartment
Twelve gallons is 24 half-gallon cartons or a stack of jugs, which is why people do not do it. Collapsible containers solve the space problem: they fold flat until the day you fill them, and four 10 liter containers fit in a drawer. The trade-off is that you have to fill them at the start of an outage, which is why "fill water" is on the first-hour checklist and why the containers live somewhere you will see them. Our three-day kit carries four of them for exactly this reason, and we will be honest that 40 liters is about 10.5 gallons, which covers four people for two and a half days at the full gallon rate or the full three days at the drinking rate. Pair them with the water heater and you are well past three days.
If you store filled containers instead, buy food-grade ones, wash them with dish soap, sanitize with a diluted unscented bleach solution, and replace the water every six months. Commercially bottled water stays sealed in its original container, somewhere cool and dark. Garages and the sunny side of the balcony are the worst places for either.
Making questionable water safe to drink
When the stored water runs out, or you are not sure what is coming out of the tap, there are three tools and they do different jobs.
Boiling kills everything biological. Bring water to a rolling boil for one full minute, or three minutes above about 5,000 feet of elevation. It does nothing for chemicals, and you need fuel and a pot, which is a real constraint in an apartment with no power.
Household bleach is the cheapest backup and the one most people get wrong. Use plain, unscented bleach with no added cleaners, and check the label for the concentration.
| Water | 6% bleach | 8.25% bleach |
|---|---|---|
| 1 quart | 2 drops | 2 drops |
| 1 gallon | 8 drops | 6 drops |
| 2 gallons | 16 drops (about a quarter teaspoon) | 12 drops (about an eighth teaspoon) |
| 4 gallons | A third of a teaspoon | A quarter teaspoon |
Stir, wait 30 minutes, and smell it. There should be a faint chlorine odor; if there is none, repeat the dose and wait another 15 minutes. If the water is cloudy, colored, or very cold, let it settle, pour it through a coffee filter or clean cloth, and double the bleach. An eyedropper belongs in every kit for this reason, and it costs less than a dollar.
Purification tablets do the same job as bleach with no measuring; follow the packet. Filters remove protozoa and bacteria and make water taste like water again, but most portable filters do not remove viruses or chemicals on their own, which is why the standard advice is a filter for taste and clarity plus boiling, bleach, or tablets for safety. We will say more about specific filters once we have documentation we trust in hand, and not before.
Three days versus two weeks
Three days is the national baseline and the right place to start. It is also, if you live somewhere with a serious regional hazard, not the end. Oregon's emergency managers ask households to be 2 Weeks Ready, which at one gallon per person per day is 14 gallons a person, or 56 gallons for a household of four. Almost nobody in an apartment stores 56 gallons, and we do not think they should try.
The two-week answer is a hybrid: store a few days, own the means to treat more, and know where the water on your block is. A rain barrel on one house, a good filter in another, collapsible containers in a third, and the water heaters in all of them add up to two weeks for a block that would never add up to two weeks for any one household. We go into this on our FAQ, and it is most of why we built a kit designed to be shared.
Questions people ask
How much water should I store per person per day?
One gallon, for drinking and sanitation combined. About three quarters of it is drinking. Store more for children, nursing mothers, anyone sick, and hot weather.
How long can I keep stored tap water?
Replace water you bottled yourself every six months. Commercially bottled water keeps much longer if it stays sealed and out of heat and sunlight.
Is water from the water heater safe to drink?
Usually, if the supply was clean before the outage. Turn off power or gas to the heater first, let it cool, and treat the water if a boil-water notice is in effect.
Can I drink pool water in an emergency?
No. Use it for flushing toilets and washing. The chemicals that keep a pool clear are not meant for drinking, and boiling does not remove them.
Does boiling water remove chemicals?
No. Boiling kills bacteria, viruses, and parasites. It concentrates chemicals slightly as water evaporates. For chemical contamination, use stored water or a filter rated for it.