Water: the supply that matters most

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.

Why so much: the body loses about 2.5 liters a day through breathing, sweat and urine, and a lot more in heat or with effort. The rest isn't a luxury: washing hands and dishes is what prevents diarrhea, which in an emergency dehydrates you faster than thirst.

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, because there's less plastic and less wasted space between them. Rotate them: use the oldest first and replace when you shop. That way you never have old water and nothing goes to waste.

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. Other plastics can leach into the water over the months, and residue from what they held never fully washes out. The most recommended plastic is HDPE, number 2 in the recycling triangle, because it's tough and doesn't pass any taste or smell to the water.
• 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. Bacteria stuck to the walls are what multiply later in stored water.

Where to store it

Somewhere dark and cool: light makes algae grow and heat ages the plastic. Away from chemicals, gasoline or paint, because plastic lets some vapors through and the water ends up tasting of them. Put it on a board or shelf, not directly on the floor, so it doesn't pick up damp or dirt and you can check it easily. If it might freeze, fill containers only to about 85%: water expands when it freezes and could burst them.

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. The chlorine in tap water slowly evaporates, and without it nothing stops a bacterium that got in during filling. 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, so you know which to use first without guessing. 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 and drain the tank from its valve. The open tap lets air in: without it, the vacuum keeps the water from flowing. Let the water cool so you don't get burned, wait for the sediment from the bottom of the tank to 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 top tap lets air in and the water left in the pipes drains down by its own weight.
• The toilet tank: the tank, never the bowl, which is in contact with waste. Only drinkable if you don't use cleaning tablets in it, because those chemicals aren't removed by purifying, and always purified.
• The bathtub: if a cut is announced or a blackout starts, fill it while water still runs. Not for drinking, since a bathtub isn't made for storing drinking water, but it solves flushing and cleaning and saves your real supply for drinking.

How to purify water

If the water is cloudy, let it settle first and pour it through a clean cloth or coffee filter. Suspended particles shield germs from bleach and clog filters, so removing them first makes everything else work better. 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, because heat kills bacteria, viruses and parasites alike. 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): at altitude water boils at a lower temperature and needs longer. It uses fuel, so save it for drinking water.

2. Bleach

Use only plain, unscented household bleach without detergents or additives: those additives aren't made to be swallowed. 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:

Stir and wait 30 minutes: chlorine needs that long in contact with the water to work. Cloudy or very cold water takes a double dose because dirt uses up part of the chlorine and cold slows it down. At the end you should notice a slight chlorine smell, a sign that some is left over and it has done its job; 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, which are much smaller than the filter's pores. 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, not fill a pot or give water to a child.

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

• Sawyer SqueezeView on Amazon ↗ (affiliate link, opens in a new tab)
• Katadyn BeFree 1 LView on Amazon ↗ (affiliate link, opens in a new tab)

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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