How much water to store for emergencies

Why the official figures differ

Every agency agrees on the idea, enough water to manage for a few days if the taps stop or the water is unsafe, but they count different things. Ready.gov’s gallon a day, about 3.79 litres, is for drinking and sanitation together, and the CDC uses the same gallon for three days with a two-week supply if possible. The UK’s Be Ready checklist, dated 15 October 2026, asks for 3 litres a day for drinking and says more is needed for cooking and washing. Get Prepared Canada says about four litres a day, Get Ready Queensland at least 10 litres per person for three days, and the Dutch government’s Denk vooruit 3 litres a day. The EU’s Preparedness Union Strategy aims for 72 hours of self-sufficiency but sets no water figure, so pick the guidance for where you live, or the larger figure if you are unsure.

The calculator multiplies your chosen figure by people and days, adds pets, and shows the same household under every country’s figure so you can see the range. It then counts the containers you need, rounding up, and the weight: a litre of water weighs about a kilogram, which matters if you store it on a shelf, in a flat with no lift, or plan to carry any of it.

Worked example

The card above is for four people and a dog for three days under US guidance. Four people × 3 days × 1 gallon is 12 gallons, or 45.4 litres. The dog adds 12 litres, at Get Prepared Canada’s 4 litres a day per average dog, for 57.4 litres in all: 15.2 US gallons, or 16 one-gallon jugs, weighing about 57 kg. The same household needs 48 litres under the UK figure (36 for the people, all of it for drinking) and 60 litres under Canada’s. Tick “hot climate” and the people’s share doubles, because Ready.gov says that in very hot temperatures water needs can double.

Who needs more water

• Children, nursing mothers and people who are ill: Ready.gov says they may need more. The CDC adds pregnant women, people who are sick, pets and anyone in a hot climate.
• Babies on formula: ready-to-feed formula avoids needing safe water to mix it. The UK checklist says ready-to-feed is best, as you may not be able to boil water to make up powdered formula safely.
• Pets: Get Prepared Canada’s figure is 4 litres a day for an average dog and 1 litre for an average cat, which the calculator uses. Ready.gov says to keep several days’ supply of water for pets, with a bowl. Ask your vet about other animals.
• Hikes and days out: water for a walk is a different calculation. Our sister site Summit Cabin works out water needs for a hike.

How to store water safely

Ready.gov suggests buying commercially bottled water and keeping it sealed in its original container in a cool, dark place; the CDC calls unopened bottled water the safest and most reliable source in an emergency, and says to observe the expiration date. If you fill your own containers, use food-grade ones, clean and sanitise them first, and replace the water every six months. Write the fill date on each container so everyone knows when the six months are up.

If the stored water runs out

The CDC’s guidance for making water safe: bring clear water to a rolling boil for 1 minute (3 minutes above 6,500 feet, about 1,980 metres) and let it cool. If you can’t boil it, use unscented household bleach that says 5% to 9% sodium hypochlorite on the label: 8 drops, or half a millilitre, per gallon (3.8 litres) of clear water, double that for cloudy, coloured or very cold water, then let it stand for at least 30 minutes. Ready.gov says not to use scented or colour-safe bleach, or bleach with added cleaners. Neither boiling nor bleach makes water safe if it contains fuel, toxic chemicals or radioactive material, so follow local advice after a flood or spill.

Common mistakes

• Storing only drinking water when you also expect to wash and flush. The US figure includes sanitation; the UK figure does not.
• Forgetting the pets. A dog can need as much as a person under the UK figure.
• Containers too heavy to move. A full 5-gallon container weighs about 19 kg. Mix in smaller bottles you can carry, which Canada suggests for the kit.
• No dates. Without a fill date, stored water gets forgotten for years.

To fit water into a whole kit with food, light and medicines, use the emergency kit list builder; for the matching meals, the food supply calculator.

General information, not medical advice. If someone shows signs of illness from drinking water, or after drinking flood water, contact a doctor or your local health service.