How much water to store, and for how many days

The totals differ by more than most people would guess

Multiply each country's own litres-per-person figure by its own horizon and the amount a household is told to store runs from 6 litres per person to 42. The lowest figure is shared by Finland, France, Italy, and Spain. The highest belongs to Austria. That is a factor of about 7, across countries with comparable infrastructure and comparable weather.

Neither is wrong. They are answers to slightly different questions: how long a supply is likely to be interrupted, and how much of the shortfall a household is expected to carry rather than the state.

What each country publishes

Portugal is the one country that sets a horizon of 72 hours and names water in the kit without ever quantifying it, so there is nothing to put in its row. The odd-looking figure for the United States is one US gallon, converted.

What the figure covers, and what it does not

Almost every one of these numbers is drinking water plus the cooking that goes with it. Washing, flushing and cleaning are on top, and they are the larger number by far: ordinary household use runs to well over a hundred litres per person per day.

That is why the guidance is survivable rather than comfortable. It is also why the practical answer to washing during an outage is usually a bucket of non-drinking water rather than more bottles.

Why there is no single right number

A site that publishes one water figure for every country has to have picked one, and the pick is wrong everywhere it is not the local one. An average of these figures would be lower than what Austria asks of its households and higher than what Switzerland asks of its own, and it would carry the authority of neither.

So the honest form of this advice names the country and names the source. If a page tells you how much water to store without telling you which government said so, it is guessing.

The figure this site plans on, and why it is higher

Where a national authority publishes less than 3 litres per person a day, which is the widely used international reference for drinking, we plan on 4 and show both numbers rather than quietly deferring.

The reason is the asymmetry. Storing more water than you need costs shelf space. Storing less does not fail gracefully. We never round an authority down, and we never restate their number as ours.

Storing it without buying anything

• Tap water in clean, sealed, food-grade containers keeps for about six months in a cool dark place. Label it with the date and swap it when the clocks change.
• Commercially bottled water keeps far longer and carries its own date. It is the lower-effort option and the more expensive one.
• Store it low and spread out. Water is heavy, a full ten-litre container is ten kilograms, and a single stack is a single point of failure.
• Anything you would use for washing rather than drinking can be stored in whatever you have, including a filled bath at the point an outage looks likely to last.