Water

How much

The agencies give slightly different numbers, so here they are side by side.

That covers drinking, simple food preparation and a little hygiene. It does not cover baths, laundry or flushing. Add more for hot weather, illness, pregnancy or nursing, and for pets. A medium dog needs about a litre a day.

A family of four for two weeks needs about 224 litres, or 60 US gallons. The calculator does the sum for your household.

What to store it in

• Store-bought bottled water is the simplest. Keep it sealed, cool and out of sunlight.
• Food-grade water containers you fill yourself. Sizes of 10 to 25 litres (3 to 7 gallons) are the largest most people can lift and pour. See stackable water containers on Amazon.
• Do not reuse milk jugs or containers that held chemicals.
• Replace water you bottled yourself about every six months, and write the date on it.

Where to keep it in a cold house

Water expands when it freezes and can split a full container. In a house with no heat, keep water in the room you are living in, leave a little air space at the top of each container, and keep it off bare concrete floors. A garage or unheated porch is the wrong place in January.

When the power goes out

1. Fill things straight away: pots, pitchers, clean buckets, the bathtub for washing and flushing.
2. On a well, the water in the pressure tank is all you get. Use it carefully.
3. The water heater tank holds clean water. A typical tank holds 150 to 300 litres (40 to 80 gallons). Turn off its power or gas first, and learn how to drain yours before you need to.
4. Listen for a boil-water notice. When treatment plants lose power or pressure, tap water may flow but not be safe.

Making water safe

Boiling is the most reliable way to kill germs. Bring clear water to a rolling boil for one minute, then let it cool. At high altitude boil longer: the CDC says three minutes above 6,500 feet, and Health Canada says at least two minutes above 2,000 metres. If the water is cloudy, let it settle and pour it through a clean cloth or coffee filter first.

Boiling needs fuel and a safe place to do it. That means outdoors on a camp stove, never indoors.

Filters remove bacteria and parasites, and some remove viruses. They differ a lot. See the water filter guide.

Disinfecting with bleach or tablets works when you cannot boil, but the right amount depends on the strength of the product, and bleach varies. Follow the EPA's or your local health authority's instructions for the exact product in your hand, linked in the sources below. Do not guess.

Where more water comes from

In a long outage, authorities set up water distribution points. Find out how your town announces them. Rain and melted snow can be collected, but treat them like any untreated water: filter, then boil. Melting snow also takes a lot of fuel, because snow is mostly air.