Emergency preparedness guide

How much water do you need per person in a power cut?

The short answer: plan for at least 3 litres of drinking water per person per day, and about 10 litres a day if you also want to cook and keep clean. For the government's three-day advice, that is 9 litres each as a bare minimum, or about 30 litres each to be comfortable.

A power cut does not always stop the taps, but it can. Water treatment and pumping both need electricity, and floods, cyberattacks and burst mains can cut supply with or without a power cut. Water is the one thing you cannot go without for long, and it is the easiest to store.

How much to store

The government's new Be Ready campaign, launched on 22 October 2026, asks households to keep three days of water, at three litres per person per day for drinking. The government's wider Prepare guidance gives about 10 litres per person per day as a comfortable figure once cooking and basic washing are included. Here is what that adds up to, per person:

How long	Drinking only (3 litres a day)	Comfortable (10 litres a day)
3 days	9 litres	30 litres
1 week	21 litres	70 litres
2 weeks	42 litres	140 litres

Multiply by the number of people in your home, then add extra for pets, and for babies if you use formula. For longer disruptions, the World Health Organization's emergency planning figures start at about 5 litres per person per day in the first month and rise towards 15 to 20 litres a day as a longer-term norm.

Where to keep it

• Buy bottled water and rotate it into normal use every 6 to 12 months, or store tap water in clean, food-grade containers with the date written on.
• Keep it somewhere cool, dark and easy to reach, not in a loft you cannot get into in the dark.
• If you get any warning, fill the bath and any large clean containers straight away. Bath water is best kept for washing and flushing. Keep your clean containers for drinking.

If your stored water runs out

• Boil it. A rolling boil for at least one minute makes water safe from germs, if you still have power or fuel to heat it.
• Use purification tablets. Chlorine tablets such as Aquatabs or Puritabs need no power. Use the dose on the pack for the size of your container, then cover it and wait a full 30 minutes before drinking.
• Clear cloudy water first. Pour it through a clean cloth. Tablets deal with germs, not dirt.

The toilet: you do not need to waste drinking water

A toilet flushes by gravity once enough water goes into the bowl quickly. If the taps are dry but the drains still work, tipping roughly half to a full bucket (about 5 to 10 litres) into the bowl in one steady pour does the job of a flush. That water does not need to be drinkable. Bath water, washing-up water and rainwater all work. Anglian Water lists toilet flushing among the sensible uses for rainwater, and says rainwater should not be used for drinking, bathing or washing dishes because it can carry harmful bacteria.

Check before you flush. Only use the bucket flush if the sewer is still working. If your area is flooded, if sewage is rising in a drain or the toilet, or if your water company or council has told people not to use their toilets, do not flush. Follow the official advice at the time.

Washing when water is short

Handwashing comes first: before preparing or eating food, and after using the toilet. Hand sanitiser and wipes are a genuine substitute when water is tight, so keep some in your kit. A flannel wash of hands, face and underarms with a cup or two of water covers the essentials.

Do this today

• Count how many people (and pets) are in your home and work out your three-day figure from the table above.
• Buy that much bottled water, or fill and label clean containers.
• Add a pack of purification tablets and a few spare bottles to your kit.
• If anyone in your home needs extra support during an outage, register with your water supplier's free Priority Services Register, so they know to check on you.

• Free printable checklist: preparing beyond three days
• The government's Be Ready advice: what it covers, and what it leaves out
• How long would UK supermarkets last in a crisis?