Emergency water storage: how much and how to purify

How much water to store

The standard reference used by preparedness experts is 1 gallon (about 4 liters) per person per day: 2 to 3 liters for drinking and the rest for cooking and basic hygiene. Several expert guides point out that this is a minimum, not a comfortable amount.

Household	3 days	2 weeks
1 person	3 gal · 12 L	14 gal · 56 L
2 people	6 gal · 24 L	28 gal · 112 L
4 people	12 gal · 48 L	56 gal · 224 L

Add more in hot weather and for babies, pregnant or breastfeeding women and sick people. For dogs and cats, allow about 1 fluid ounce per pound of body weight per day (60 ml per kg). Get your exact numbers with the calculator.

Containers

Bottled water

The easiest way to start. Larger jugs take up less space per gallon than small bottles. Rotate them: use the oldest first and replace when you shop.

Your own containers filled with tap water

Cheaper in the long run. The rules:

Food-grade containers only, which have never held anything but food. The most recommended plastic is HDPE, number 2 in the recycling triangle.
Never milk or juice jugs, even washed: organic residue breeds bacteria and the plastic is too thin.
No more than 5 to 7 gallons per container. Water weighs over 8 pounds per gallon: you won't be able to move anything bigger.
Sanitize before filling: wash with soap and water, rinse with a solution of 1 teaspoon of unscented bleach per quart of water, shake, empty and let air-dry.

Where to store it

Somewhere dark and cool, away from chemicals, gasoline or paint, because plastic lets some vapors through. Put it on a board or shelf, not directly on concrete. If it might freeze, fill containers only to about 85%: water expands when it freezes.

How often to rotate it

Water itself doesn't go bad. What goes wrong is the container or what gets into it. In practice:

Bottled: follow the best-by date and rotate.
Tap water in a clean container: replace it every 6 to 12 months. Some expert guides stretch this to two or three years with good containers stored in the dark, but changing it yearly costs nothing and removes doubt.

Label each container with the fill date. If it smells odd or you see something floating, purify it before drinking or use it for flushing.

Hidden water in your home

If an outage catches you without a supply, your home holds more water than you think:

The water heater: a typical tank holds 30 to 80 gallons. Turn off its power or gas, close the cold-water inlet, open a hot tap elsewhere in the house to let air in, and drain the tank from its valve. Let the water cool and the sediment settle, then purify it.
The pipes: after closing the main valve, open the highest tap in the house and collect the water from the lowest one.
The toilet tank: the tank, never the bowl. Only drinkable if you don't use cleaning tablets in it, and always purified.
The bathtub: if a cut is announced, fill it. Not for drinking, but it solves flushing and cleaning.

Water for everything else

Pool water is not drinkable, even when treated, because of stabilizers and chemicals. But it works for flushing, mopping or washing. And if you can't use the toilet, set up an emergency toilet.

How to purify water

If the water is cloudy, let it settle first and pour it through a clean cloth or coffee filter. None of these methods removes chemicals like fuel or pesticides: if you suspect that kind of contamination, don't drink it.

1. Boiling

The most reliable method. Bring the water to a rolling boil and keep it there for at least 1 minute, or 3 minutes above 6,500 feet (2,000 meters). It uses fuel, so save it for drinking water.

2. Bleach

Use only plain, unscented household bleach without detergents or additives. Check the label for the concentration and follow its instructions if it gives any. As a general reference for bleach of around 5–6% sodium hypochlorite:

Amount of water	Clear water	Cloudy or very cold water
1 quart or liter	2 drops	4 drops
1 gallon	8 drops	16 drops
5 gallons	½ teaspoon	1 teaspoon

Stir and wait 30 minutes. You should notice a slight chlorine smell; if not, repeat the dose and wait another 15 minutes. Bleach loses strength over time: replace the bottle in your kit every year.

3. Purification tablets

Light and easy to store. Respect the manufacturer's waiting time: some parasites, such as Cryptosporidium, need up to several hours with certain products. Check the expiry date.

4. Portable filters

They treat water instantly, and a small one can last thousands of gallons. Note: most remove bacteria and protozoa, but not viruses. If the water could be contaminated by sewage, as after a flood, combine the filter with bleach, tablets or boiling. Experts advise against straw-type filters as your main solution: they only let you drink directly from the source.

Two lightweight filters highly rated by experts, which screw onto standard bottles:

The expert tip

Always have two different ways to purify water, for example a filter and tablets. If one fails, you have the other.

Common mistakes

Storing water in milk or juice jugs.
Buying a 55-gallon drum that nobody can move or refill easily.
Storing water next to the lawnmower gasoline or cleaning products.
Using scented bleach or bleach with detergent.
Counting on the water heater as your main reserve: it's plan B, not plan A.

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