The UK government's Be Ready checklist puts drinking water first for a reason. A power cut is uncomfortable. A water interruption, or a boil-water notice during a power cut, is a genuine problem within hours. Yet almost nobody keeps water at home, because the tap has never failed.
The number: 3 litres per person per day
That is the government's figure for drinking. Over three days it means 9 litres per person. For a household of four, 36 litres: eighteen 2-litre bottles, or three of the 6-litre multipacks most supermarkets sell. It sounds like a lot until you stack it; it is a cube about 40 cm on a side.
Cooking and basic hygiene need more. The guidance does not set a figure, but adding roughly 4 litres per person per day for washing hands, brushing teeth, rinsing a pan and a flannel wash is a comfortable target. You do not need to buy this as bottled water: it can be tap water in clean containers, or water you fill into the bath and clean buckets when a warning gives you a few hours' notice.
What to buy
Where and how to store it
Cool, dark, off the floor of a garage
Heat and sunlight degrade plastic and encourage algae. The bottom of a kitchen cupboard, the hall cupboard or under a bed are all better than a sunny conservatory or a garage that bakes in summer.
Away from chemicals and fuel
Plastic is slightly permeable. Do not store water next to petrol, white spirit, bleach or strong-smelling cleaning products.
Leave it sealed
Opened bottles should be used within a day or two. The kit water stays sealed until you need it.
Rotate it
At each six-month check, move the oldest bottles into everyday use and replace them. Write the date on the pack with a marker.
How long does it keep?
Sealed commercial bottled water does not go off. UK bottles carry a best-before date, usually one to two years, because the plastic can slowly affect taste, not because the water becomes unsafe. Tap water you have stored yourself in clean containers is best replaced every six months. If stored water smells or tastes odd, boil it before drinking or use it for flushing and cleaning.
Making water safe
If the mains supply is interrupted, your water company will issue instructions and, for longer outages, set up bottled water stations. Customers on the Priority Services Register can have water delivered. If you are told to boil water, or you are unsure:
- Boil it. A rolling boil for one minute, then cool. A camping stove outdoors or a gas hob with a match works in a power cut. Never use a camping stove or barbecue indoors.
- Treat it. Purification tablets on clear water, following the pack timing.
- Filter first if cloudy, through a clean tea towel or coffee filter, then boil or treat.
Drink from a hot water tank or central heating system, use water from a bath that has been standing uncovered for days for drinking, or rely on a jug filter to make unsafe water safe. Jug filters improve taste; they do not disinfect.
Water for babies, pets and medical needs
Babies need more water per kilo than anyone. Bottled water labelled low in sodium is suitable for making up formula once boiled, but ready-to-feed cartons remove the problem altogether. Pets need about a litre a day for a cat or a medium dog, more in heat. If someone uses a CPAP machine, a nebuliser or home dialysis, check the manufacturer's advice on water and talk to your care team about a contingency plan now, not during an outage.
Saving water during an interruption
- Do not flush for urine. Use a bucket of bath or rainwater to flush when needed.
- Hand sanitiser and wet wipes replace most hand washing.
- Paper plates and cups for three days are not glamorous but save litres of washing up.
- Eat tinned food that comes in its own liquid (beans, fruit, sweetcorn, soup) and you drink less.
Recommended water containers and purification tablets are on the recommended kit page. None of the links on this site currently earn us a commission; if that changes we will say so.
Common questions
Does bottled water go off?
Sealed bottled water does not spoil. The best-before date on UK bottles relates to the plastic and taste, not safety. Kept cool, dark and sealed, it is fine well past the date, but rotating it into normal use every six to twelve months keeps it tasting fresh.
Can I just fill the bath when there is a warning?
Yes, and it is a sensible top-up for flushing and washing. Do not rely on it for drinking unless you have clean containers with lids. A bath holds around 80 litres, which covers a family's non-drinking needs for several days.
Is tap water stored in old bottles safe to drink?
Tap water stored in thoroughly cleaned food-grade containers with tight lids, kept cool and dark, is generally fine for drinking for around six months. Replace it twice a year at the kit check. Use proper water containers rather than milk bottles, which are hard to clean.
How do I make water safe if I run out of bottled?
Bring it to a rolling boil for one minute and let it cool. If you cannot boil, water purification tablets work on clear water in about 30 minutes. Cloudy water should be filtered through a clean cloth first. Follow any boil-water notice from your water company.