You need more water than you think, and it's cheap

Store at least 3 litres of drinking water per person per day, the WHO survival minimum (GOV.UK Prepare, checked 26 August 2026). Three days is 9 litres each, about £1.50 from any supermarket. A week for a family of four is 84 litres, so most households store three days and plan to fill pans for the rest.

How much water do you actually need?

The government’s Prepare campaign gives two numbers. The survival figure: 2.5 to 3 litres of drinking water per person per day, which it notes is the World Health Organisation’s recommendation. The comfort figure: 10 litres per person per day, which also covers basic cooking and hygiene.

Use the 3 litre figure for what you store, and the 10 litre figure for what you plan to find on the day: filling the bath while there’s pressure, collecting from a bowser, reusing washing-up water for the loo. Nobody keeps a week of comfort-level water in a British kitchen, and nobody needs to.

The arithmetic, done honestly

At 3 litres per person per day, here is what storage actually looks like.

Two things jump out. First, three days is genuinely small: for a couple, 18 litres is three supermarket multipacks on one cupboard shelf. Second, a full week is genuinely heavy: a litre of water weighs a kilogram, so a week for a family of four is 84 litres and roughly 84 kg. That’s why the sensible plan is to store three days, then extend on the day by filling everything that holds water the moment supply looks shaky. At the comfort level of 10 litres a day, three days for four people would be 120 litres, which is a plan for taps and bowsers, not cupboards.

Water disruptions long enough to need the full week are rare, but they happen: around 24,000 homes in and near Tunbridge Wells lost supply or were under a boil notice for about two weeks in late 2025. The households with a few days stored skipped the worst of the morning queues. Our water-off scenario guide walks through such a week hour by hour.

What does it cost?

Very little, which is the point of this page’s title. A supermarket 6 × 1.5 litre multipack is exactly 9 litres, one person’s three days, at ≈ £1.50 (typical supermarket price, Aug 2026 — check monthly). Three days for a family of four is four multipacks, ≈ £6. Even the intimidating full week for four is ten multipacks, ≈ £15. Water is the cheapest item in the whole emergency kit, and the one you’d miss first.

Bottled water or containers?

Start with bottles: sealed, dated, no maintenance, and you can buy them with the weekly shop. Add a couple of rigid containers with lids later, and store them empty, clean and dry; their job is bowser trips and last-minute filling, not sitting full for months.

Where should you keep it?

Somewhere cool, dark and easy to reach: under the stairs, the bottom of a wardrobe, the floor of a larder. Keep it away from direct sunlight and away from strong-smelling products like bleach, paint and petrol, and follow the storage line printed on the pack. GOV.UK’s food labelling guidance makes the general point that badly stored food “could reduce in quality before the best before date”.

You may read online that water should never be stored on a concrete floor. We could not find any UK authority that says this for modern sealed bottles, and garages and cellars are otherwise good cool spots. [VERIFY: whether concrete storage affects sealed bottled water — packaging industry or FSA guidance] A slat, mat or a bit of shelf under the pack costs nothing if you’d rather not test it.

Weight is not a structural worry at these quantities: 36 litres spread along a cupboard floor loads it less than a bookcase. Just keep heavy packs at floor level rather than overhead.

Rotation: does stored water go off?

Bottled water carries a best-before date, and best-before dates “relate to quality” rather than safety; after them, food and drink “is usually safe to eat but may not be of the same quality” (GOV.UK food labelling guidance, checked 26 August 2026). So rotation is about taste, not danger, and it’s easy: write the purchase month on each pack with a marker, and when the clocks change in March and October, drink the oldest packs with the weekly meals and replace them on the next shop.

Flats: the weight problem, solved slowly

If you live up two flights with no lift, the arithmetic above meets the stairs. The answer is never one heroic trip. One 9-litre multipack added to the weekly shop builds a family’s three days inside a month, one comfortable carry at a time. Keep two 5-litre bottles per person as a sensible ceiling for cupboard space, split storage between rooms if one cupboard can’t take it, and stop before the bag count exceeds what you can carry in one journey.

Filling at the last minute

If the water is still flowing but trouble is coming, ten minutes at the taps roughly doubles your stores.

1. Fill the kettle, then every saucepan, jug and bottle with a lid. Lids matter: this is drinking water.
2. Then fill the bath and a bucket or two. Bath water is for flushing and washing, not drinking.
3. If a boil water notice arrives later, boiled and cooled water keeps in a clean container in the fridge, and the Drinking Water Inspectorate says to discard it if not used within 24 hours.

What this asks of your body

Water is the heaviest thing on this site. One multipack is 9 kg, a full 25-litre container is 25 kg, and a bowser queue means carrying whatever you collect all the way home. Carrying two loaded bags up two flights without stopping is the first of the five Ready Body tests, and it was chosen with exactly this cupboard in mind. If a multipack in each hand sounds impossible, start the four-week plan on that page before you need it.

Frequently asked questions

How much water should I store per person?

At least 3 litres per person per day for drinking, the WHO minimum quoted by the government’s Prepare campaign, so 9 litres each for three days. The 10 litres a day that covers cooking and hygiene is something you plan to collect or fill on the day, not store.

Is 9 litres per person really enough?

It covers drinking for three days, which sees out most UK supply interruptions. It doesn’t cover washing, cooking or flushing, which is why the first move in any outage is filling pans and the bath while pressure lasts. Store three days; extend on the day.

Can I drink bottled water after its best-before date?

The date is about quality, not safety: GOV.UK’s guidance says food past its best-before “is usually safe to eat but may not be of the same quality”. Rotate at the clocks change so the question rarely comes up, and let sight, taste and smell guide you.

Can I store tap water instead of buying bottled?

You can fill clean, lidded containers at need, and boiled water keeps 24 hours in the fridge during a boil notice (DWI). We found no official figure for how long plain stored tap water keeps. [VERIFY: storage life of tap water in containers — DWI or your water company] Sealed, dated bottles are simpler.

Where do I put 36 litres in a small flat?

Split it: one multipack under the sink (away from cleaning products), one in each wardrobe, one under a bed. Nothing needs to be together as long as you know where it all is. Two 5-litre bottles per person is a sensible ceiling for any one cupboard.

What about water for pets?

During a boil water notice, the Drinking Water Inspectorate’s advice is that pets get boiled and cooled water, the same as people. Bottled water is fine as a practical alternative. There’s no official per-pet storage figure, so we simply add a couple of extra litres to the family total and rotate it the same way.

How do I carry it all home?

You don’t, not in one go. A 9-litre multipack per shopping trip is one comfortable carry, and a family’s three days is built in a month. If you drive, load the boot; if you don’t, a shopping trolley or a rucksack turns 9 kg into an easy walk.

Sources & review

• UK Government, Prepare campaign: Get prepared for emergencies. Checked 26 August 2026. The 2.5–3 litres per person per day WHO minimum and the 10 litres per person per day comfort figure.
• Drinking Water Inspectorate: Receiving a boil water notice. Checked 26 August 2026. Boiled water stored in a clean container in the fridge and discarded after 24 hours; boiled and cooled water for pets.
• GOV.UK: Best before and use-by dates. Checked 26 August 2026. Best-before dates relate to quality, not safety; storage affects quality; sight, taste and smell after the date.

The Tunbridge Wells figures follow our sourced write-up in the water-off scenario guide. Prices marked “typical” were estimated on 26 August 2026 and should be checked monthly. Awaiting review (reviewedBy: TBC), and two [VERIFY] tags need resolving before publication.