How Much Emergency Water Do You Really Need?

Four litres per person per day is the figure used by emergency management agencies around the world. It is not a suggestion or a safety margin — it is the practical minimum for drinking, food preparation and basic hygiene.

Two of those litres are for drinking. The rest covers cooking, brushing teeth and washing hands. If you have ever tried to cook rice, make coffee and clean up for four people on two litres, you will understand why the other two litres exist.

How it scales for a household

| Household | 72 hours | 7 days | 14 days | | --- | --- | --- | --- | | 1 adult | 12 L | 28 L | 56 L | | 2 adults | 24 L | 56 L | 112 L | | 2 adults + 2 children | 42 L | 98 L | 196 L | | 4 adults | 48 L | 112 L | 224 L |

Children are counted at roughly three-quarters of an adult for water and food. Pets are separate: allow about 1.5 litres per medium dog per day, and don't forget them — they cannot ration.

Storage is the part people skip

The arithmetic is easy. Holding 100 litres of drinkable water is the hard part, and it is where most households quietly fail. Bottled water sounds simple, but 100 litres is 50 large bottles, and plastic bottles do not stack well, get brittle, and take on flavours if stored somewhere warm.

Rigid containers with a spigot solve the practical problem: you can pour a glass without lifting 20 kg overhead, and you can drain, clean and refill them. Two 26-litre containers give a family of two about a week of drinking and hygiene water.

Sanitise new containers before the first fill, label each one with the date, and rotate stored water every six to twelve months. Store it out of sunlight and away from fuel, paint and garden chemicals — plastic is not a barrier to odour.

When the mains fail

Stored water runs out faster than people expect, especially in summer. That is why a filter belongs in every plan: it gives you a second source rather than a fixed quantity.

A filter removes bacteria and protozoa, not dissolved chemicals or salt. If chemical contamination is suspected, follow official boil-water guidance rather than treating the water yourself.

If a boil-water advisory is issued, stop drinking from the tap immediately — including for ice and brushing teeth — and follow the utility's guidance on when and how to flush the system afterwards. Replace any filter that was in use during the advisory.

The short version

Store four litres per person per day for at least 72 hours, in containers you can pour from. Add 1.5 litres per pet per day. Buy a filter so you are not limited by what you have stored, and rotate the whole supply twice a year when you change your smoke alarm batteries.