Emergency Water Calculator

Calculate your reserve

Your water result

What baseline does this calculator use?

The drinking-only setting uses two litres of fluid per person per day. That matches current UK public-health messaging for a national power outage, which tells adults and most older children to try to drink at least two litres of fluid a day. The broader five-litre setting adds a three-litre allowance for cooking and basic washing; that figure is used by some UK local emergency-planning guidance as a practical household preparedness target.

These are planning numbers, not medical instructions. Fluid needs vary with age, temperature, pregnancy, breastfeeding, illness, activity and medication. Babies who use formula, people with particular medical needs and pets require separate planning. The calculator includes an “extra litres per day” field precisely because a single universal number cannot cover every household.

Why litres disappear faster than people expect

Drinking is obvious. Hand washing, preparing food, brushing teeth and cleaning essential equipment are not. Even a cautious household can burn through stored water surprisingly fast once every use has to come from a bottle. That is why a reserve should be measured rather than estimated by eye.

For two people over three days, the two-litre drinking baseline is twelve litres before any cooking, hygiene or pet requirement is added. The broader five-litre planning level is thirty litres. Seeing that difference is useful because it forces a household to decide which uses will be protected and which can be reduced if water becomes scarce.

AI doomsday scenario: the problem is distribution

In the fictional nightmare, the country does not need to “run out of water” for households to suffer. Pumping, telemetry, treatment controls, electricity, road transport or digital coordination can fail independently. A cyber incident that forces operators to isolate automated systems could create local outages even while reservoirs remain full. If the same incident disrupts payments and logistics, bottled water can become difficult to obtain at exactly the moment demand spikes.

The frightening version is uncertainty. One neighbourhood receives a genuine boil-water instruction while another sees an AI-generated fake. Tankers are announced, then redirected. Social media fills with fabricated contamination maps. In that environment, a measured household reserve buys time to verify information rather than joining the first queue created by an unverified message.

Storage matters as much as the number

UK Prepare recommends commercially bottled water for longer storage because it is sealed in food-grade packaging. Rotate supplies according to the bottle guidance and store them somewhere cool and practical to access. If you use refillable containers, they need to be suitable for drinking water and managed hygienically; do not assume any container that holds liquid is appropriate for long-term potable-water storage.

The calculation is also not permission to hoard. It is a way to build a modest buffer before an emergency. Water companies have obligations to provide alternative supplies during interruptions, but distribution can still take time and people with additional needs may require priority support. A household reserve reduces pressure during that gap.