PrepEmergency water storage calculator
Work out how much water to keep at home, what that looks like in bottles, and how many days the water you already have would last. Nothing leaves this browser.
Who's at home?
Saved in this browser for the other tools.
How long, and how much?
From preppantry.app. Checked 2 November 2026. Independent tool, not official advice.
How it works
We multiply the people in your household by the litres per person per day, then by the number of days. Adults and children count the same here, because the government figure is per person. Pets are added on top. We round up, and the bottle counts are rounded up to whole bottles.
3 litres a day is drinking water only. It's the figure in the government's Be Ready checklist, which adds that more would be needed for other tasks such as cooking and washing. 10 litres a day is a British Red Cross figure, not a government one. It covers drinking plus basic cooking, washing and hygiene. Both are planned over 3 days.
Which should you choose? Start with 3 litres, because drinking comes first. Move to 10 litres if you've got the space, or if your household would struggle without water for washing, such as with a baby or someone who is ill.
Hot weather: Ready.gov, the US government's preparedness site, says water needs can double in very hot temperatures. The UK sources give no figure, so the hot-weather option uses the US one and doubles the amount for people. It's an upper planning figure, not a rule.
Pets: no official source gives a volume, UK or US. We use 1 litre per pet per day, the figure the Prep app starts with. It's an estimate. A large dog may need more and a cat much less, and it doesn't change in the hot-weather option.
Storing it: keep shop-bought water sealed and go by its best-before date, which Water UK says is usually at most 2 years. If you fill your own clean, food-safe containers, change the water every 6 months. That timing comes from the US CDC and Ready.gov, as we found no UK figure for it. Be Ready asks you to check your supplies every six months anyway.
Example: two adults, one child and a dog over 3 days at 3 litres each is 27 litres for the people and 3 for the dog, 30 litres in all. That's 15 of the 2 L bottles, or 6 of the 5 L bottles.
Common questions
How much water should I store per person?
The UK government's Be Ready campaign says 3 litres per person per day for 3 days, for drinking. That's 9 litres per person. The British Red Cross says around 10 litres a day if you include basic cooking, washing and hygiene.
Is it 3 litres or 10 litres?
Both, for different things. 3 litres is drinking water. 10 litres also covers basic cooking, washing and hygiene, and it's a British Red Cross figure, not a government one. Start with 3 and add more if you can.
Do children need the full 3 litres?
Be Ready's figure is per person and doesn't split adults from children, so this calculator counts everyone the same. The days-ready calculator on this site uses the Prep app's figure of 2 litres for a child, so its answer can differ. Use the higher figure if you're planning from scratch.
What about the Chief Medical Officers' 2 litres?
Their script for a national power cut says to try to drink at least 2 litres of fluid a day, which can include drinks other than water. That's a target during a shortage. It isn't a figure for how much to store, and Be Ready's 3 litres is.
How long does stored water last?
Follow the best-before date on bottled water. Water UK says the shelf life is usually at most 2 years. The US CDC and Ready.gov say to replace water you've bottled yourself every 6 months.
What if we have a baby or someone needs water for a medical device?
Be Ready says to keep extra for baby formula, medical devices and pets, without giving amounts. Ready-to-feed formula is best, as you may not be able to boil water for powdered formula. If a device needs water, talk to your care team about a plan.
Sources
- Be Ready checklist (3 litres per person per day, 3 days)
- Be Ready: water supply interruptions
- British Red Cross: prepare an emergency kit (around 10 litres with basic cooking, washing and hygiene)
- UK Chief Medical Officers: water and sanitation scripts (16 December 2025)
- Water UK: storage and use of bottled water (TGN 11)
- Ready.gov: water (last updated 22 February 2021)
- CDC: creating and storing an emergency water supply (27 June 2025)
Contains public sector information licensed under the Open Government Licence v3.0.
Checked on 2 November 2026. This is an independent tool and not official advice. See sources and method.