The one-gallon-per-person-per-day figure comes from FEMA guidance and has been repeated so often it has become the default answer to water storage questions. It is a useful starting point, but it accounts only for drinking and basic sanitation. It does not account for cooking, washing dishes, pets, hot weather, physical exertion, or medical needs. Treating it as a complete answer leaves most households underserved.
The correct number for your household is higher than the FEMA baseline, and calculating it takes about five minutes.
Calculate Your Household's Actual Needs
Start with the base figure and add for each variable that applies to your household. The calculation below uses a 14-day supply as the target — long enough to cover the duration of most regional disruptions without requiring you to store an impractical amount.
Run the same calculation for your own household. Adjust the pet line for your actual animals — a large dog drinks close to a gallon a day in warm weather. Add the climate buffer if you are in a region where summer temperatures regularly exceed 90°F. Add more if anyone in the household has a medical condition that increases fluid needs.
Sanitation water — flushing toilets if municipal water is down, basic wound cleaning — is not included in any of the figures above. If you have reason to expect extended municipal water loss, budget an additional gallon per person per day for sanitation. In a two-week outage, sanitation water can exceed drinking water in total volume.
How to Store It
The container matters. Not all plastic is safe for long-term water storage, and some containers that are food-safe for other purposes leach compounds into water over time.
Food-grade HDPE containers (marked with recycling code 2) are the standard for water storage. Seven-gallon WaterBrick containers stack efficiently and hold a manageable weight per container — about 58 pounds each at capacity, which one person can move. Fifty-five-gallon drums store more volume but require a hand pump for access and are difficult to move once filled.
Never use containers that previously held non-food substances, milk jugs (HDPE but porous enough to harbor bacteria), or any container not rated food-grade. The investment in proper containers is small relative to the cost of contaminated water during an emergency.
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Tier 1 Use food-grade HDPE containers only 7-gallon containers are the practical sweet spot — manageable weight, stackable, widely available.
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Tier 1 Store in a cool, dark location Heat and UV light degrade container integrity and promote bacterial growth. A closet, garage interior, or basement is correct. A car trunk is not.
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Tier 1 Label each container with the fill date Rotate every 6 months. Commercially treated tap water stored in sealed food-grade containers stays safe considerably longer, but 6-month rotation keeps the habit consistent with go-bag maintenance.
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Tier 1 Keep containers off concrete floors Concrete can leach chemicals into plastic over time through a process called permeation. Store on shelving or pallets.
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Tier 2 WaterBOB bathtub bladder as overflow capacity Stores flat until needed. Fills a standard bathtub with up to 100 gallons when a situation is escalating. Fill it before municipal water is affected — once it's gone, it's gone.
How to Purify More When You Run Out
Stored water covers the first phase of a disruption. Purification covers everything after. Having a purification method means your stored supply is a starting point, not a hard ceiling.
Boiling is the most reliable method and requires no equipment beyond a heat source and a container. Bring water to a rolling boil for one minute — three minutes at elevations above 6,500 feet. This kills bacteria, viruses, and parasites. It does not remove chemical contaminants or heavy metals, which is worth knowing if your local water source may be chemically compromised.
Filtration handles biological contaminants through a physical barrier. A Sawyer Squeeze or LifeStraw filter removes bacteria and protozoa down to 0.1 microns — enough for most natural water sources. Filters do not remove viruses, which are smaller than the filter pores. In the US, most surface water does not carry viral contamination at high levels, but combining filtration with a purification tablet removes the uncertainty.
Chemical purification using unscented liquid chlorine bleach (6% to 8.25% sodium hypochlorite) kills bacteria and viruses. The ratio is 8 drops per gallon of clear water, 16 drops for cloudy water. Stir, let stand for 30 minutes before drinking. The treated water should have a faint chlorine smell — if it does not, repeat the dose and wait another 15 minutes. This method does not work reliably against Cryptosporidium, a parasite that requires boiling or a filter rated for cysts.
Filter to remove particulates and protozoa, then treat chemically or boil to kill viruses. In most emergency scenarios within the US, filtering alone is sufficient. Where the water source is unknown or potentially contaminated, filter then treat — do not rely on either method alone.
The Starting Point
Run your household's calculation. Buy enough food-grade containers to hold that volume. Fill them, label them, put them somewhere cool and dark. Set a 6-month calendar reminder to rotate. That is the complete water storage task — it takes one afternoon and does not need to be revisited for six months.
Add a Sawyer filter and a bottle of unscented bleach to your storage area and the ceiling on your water supply effectively disappears. Any water source within reach becomes usable.