Run the numbers

§AStress test

What runs out first?

Enter what's in the house today. We assume what every national figure assumes: no mains water, no power and no shops.

Household: 2 people. Change

Compare with

Water, in litresBottled or stored. Not the tap.Tins and jarsCounted at about 300 kcal eachOur estimateDry staples (kg)Rice, pasta, oats: about 3,500 kcal/kgOur estimateOther food (days)Your own estimate of the rest of the cupboardI can cook without mains powerOtherwise dry staples count as zero. Camp stoves are outdoors only.Medicines (days)Prescriptions, if anyone takes themPower bank chargesOne full phone charge a day, used sparinglyOur estimatePhones

First to run out

Food, within a day

Food0.4daysshort

Water0.6daysshort

Phone power1dayshort

Medicines7days

Short of 7 days Reaches 7 daysDays along the bottom

To reach 7 days

More water: 64 L
More food: 29,000kcal

Tackle these in order: food, water, phone power. Add a little on each normal shop.

A rough model, not a guarantee. Food in the fridge isn't counted, because it lasts about 4 hours without power.

§BWater treatment

Make water safer

Only when your local authority hasn't given other instructions, and you have no safe stored water. If they issue a notice, follow that.

Bleach

Regular, unscented bleach only. These are the EPA's own rows, and we don't interpolate between them.

How much clear water?

Strength on the bottle

Different strength on your bottle? This tool only covers these two. Check the label, your local authority or the EPA page.

Add

6 drops

1. Cloudy? Let it settle and filter it first.
2. Add the bleach and stir.
3. Wait 30 minutes. It should smell slightly of chlorine.
4. No smell? Repeat the dose and wait another 15 minutes.
Double the dose if the water is cloudy, coloured or very cold.

Source: US EPA ↗

Boil

The most reliable option if you have a safe way to heat water. Let it cool before drinking.

Your altitude: 100 m

Sea level4,000 m

Rolling boil for

1 min

1 minute, or 3 at altitude. Sources differ on the cut-off: the EPA says above 5,000 ft and gives that as 1,000 m, and the CDC says 6,500 ft. We use 1,000 m, the lowest of these, to be cautious.

Won't fix it

Boiling and bleach don't remove chemicals or fuel. If you suspect either, don't drink it.
Portable filters don't remove viruses. Add a disinfectant or boil.
Chlorine and iodine tablets don't reliably kill Cryptosporidium.
Baby formula: use bottled water first if you have it.

§CKeep it fresh

Set it, then forget it for 6 months

How often to check your reserve
6 months	Replace home-filled water. Check your kit, batteries and dates. FEMA, Dutch and UK governments
2 months	Rotate pet food. ASPCA
As you go	Eat what you store, and replace it on your next normal shop. Japan MAFF, Sweden
When they grow	Check nappy sizes and baby food. Our suggestion

Repeats every 6 months. Stays on your device.