UK Emergency Water Storage Calculator

How much water would your household have if the mains supply stopped today? Use this emergency water storage calculator to estimate your drinking-water and hygiene requirements, record what you already have stored and see how many days of cover it could provide.

The calculator separates drinking water from non-potable water that may be used for suitable washing, cleaning and sanitation tasks. It can also account for pets, water butts, portable containers and your chosen sufficiency target.

UK Government emergency-planning guidance says that a minimum of around 2.5 to 3 litres of drinking water per person per day is needed for survival. Around 10 litres per person per day provides greater comfort by allowing for basic cooking and hygiene as well. Use the standard figures or enter your household’s own estimated consumption.

How much emergency water should you store?

There is no single quantity that will suit every household. The amount you need depends on the number of people in the home, how long an interruption lasts, whether you have pets and how much water you intend to reserve for cooking, washing and sanitation.

For drinking water, the UK Government’s Prepare guidance refers to a survival minimum of approximately 2.5 to 3 litres per person per day. A household of four using the upper 3-litre figure would therefore require 36 litres of drinking water for three days, or 84 litres for seven days.

Drinking water and non-potable water are different

Drinking water should be safe for consumption and food preparation. Non-potable water is not intended for drinking, but may still be useful for appropriate cleaning, washing and toilet-flushing tasks.

Keeping these supplies separate is important. A full water butt may provide considerable sanitation capacity, but it does not remove the need to keep a suitable supply of safe drinking water.

What counts as stored drinking water?

The calculator lets you record common UK retail bottle and pack sizes, including 12 × 500ml packs, 6 × 1.5-litre packs and 6 × 2-litre packs. It also accepts larger food-safe water containers.

Only count sealed or properly stored water that you would be willing to use during an emergency. Check containers regularly for damage, leaks or contamination, and rotate commercially bottled water in line with its date and storage instructions.

What can be included as non-potable water?

Non-potable storage may include dedicated 5, 10, 20 or 25-litre containers, as well as water butts and larger tanks where the property has suitable outdoor space.

Untreated rainwater should not automatically be treated as drinking water. Its suitability for any particular use depends on the collection system, storage conditions and any treatment applied.

Should you prepare for three days or longer?

A three-day target provides a useful starting point for a short disruption. Seven or fourteen days offers considerably more resilience but requires more storage space, stronger containers and a practical plan for moving and rotating the water.

The calculator therefore shows both your selected target percentage and the number of days your current supply may cover. It also provides a restricted-use estimate based on half the selected daily allowance.

Remember the weight of stored water

One litre of water weighs approximately one kilogram before the weight of the container is added. A full 20-litre container will therefore weigh around 20kg, while a 210-litre water butt holds more than 200kg of water.

Spread drinking water across several manageable containers rather than relying entirely on one large vessel. This makes supplies easier to carry, rotate and isolate if one container becomes damaged or contaminated.

Emergency water storage questions