How Much Water Should Your Family Store? The Real Calculation

The official UK government guidance says store one litre per person per day. That figure is taken directly from survival medicine literature and represents the absolute minimum to keep a sedentary adult alive in a temperate climate.

It is not a useful planning figure for a real family.

One litre per person per day does not include cooking. It does not include hand washing. It does not include brushing teeth, cleaning a wound, preparing a baby's bottle, or having a cup of tea. It is the amount you need to not die. Your household needs more than that.

This guide gives you a real calculation, explains where each litre goes, and tells you what a sensible household target actually looks like.

Where Your Daily Water Actually Goes

The maths are straightforward once you break down usage by category:

Drinking: 2 litres per adult per day. The standard medical guidance for drinking water in a temperate climate is 1.5-2 litres. Use 2 litres as your figure: it accounts for slightly elevated activity during an emergency (carrying things, stress, disrupted sleep) and the reality that children drink more in warm weather.

Cooking: 1-2 litres per household per day. Most cooked food requires water: boiling pasta, making rice, soups, hot drinks. A family of four cooking from scratch uses approximately 1.5-2 litres per day on food preparation alone. If you are relying on tinned or dehydrated food (which requires hot water to reconstitute), this figure is similar.

Basic hygiene: 2-3 litres per person per day. Hand washing after toilet use (critical for preventing illness spread in a confined space): approximately 0.5 litres per wash, 4-6 washes per day = 2-3 litres. Tooth brushing: 0.25 litres. Basic face washing: 0.5 litres. This adds up to 3-4 litres per person before you consider anything else.

Wound care and sanitation: 0.5-1 litre per day. Any injury, illness, or medical need requires clean water for treatment. During a disruption, the risk of minor injury is higher than normal. Budget for this.

Total realistic daily figure per person: 5-6 litres (1.3-1.6 gallons).

For a family of four, the practical daily requirement is 20-24 litres (5-6 gallons). The official 1-litre guidance would leave your family dehydrated, unable to cook properly, and at elevated risk of secondary illness from poor hygiene.

The Kate Calculation

I use 6 litres per person per day as my household planning figure. That is 24 litres per day for a family of four, which rounds to 25 litres for easy maths.

This figure allows: - Adequate hydration for adults and children - Cooking one proper hot meal per day - Regular hand washing (critical for illness prevention in close quarters) - Basic hygiene that maintains dignity and morale - A buffer for minor medical needs

It does not allow: baths, showers, laundry, or toilet flushing (if mains pressure fails). Those are legitimate concerns for a longer outage, but they are not addressable from stored water at household scale: at 25 litres per day, water for flushing alone would add 50+ litres per day for a family of four.

Target Storage by Duration

Apply the 25 litres per day figure to different planning horizons:

Start with 72 hours. That is three 25-litre containers or equivalent: achievable immediately. Then build toward two weeks.

The two-week target is the one I recommend for most families. It covers: - Flooding events that contaminate local water supply (typically resolved within 1-2 weeks) - Extended power cuts that disrupt water pressure (rare beyond 1 week in the UK/US) - Supply chain disruptions affecting treatment chemicals at water works - Any scenario where you are asked to shelter in place for an extended period

Beyond two weeks, you are in territory where mains supply is likely restored or you have another water source available (filtered rainwater, local spring). The two-week target is the point of diminishing returns for most households.

Adjusting for Your Household

The 25-litres-per-day figure assumes a family of four adults or near-adults. Adjust for:

Young children (under 5): Reduce drinking water requirement to 1-1.5 litres per child. But increase hygiene water: nappy changes and hand washing around young children require more water, not less. The net adjustment is approximately zero.

Elderly or medically vulnerable household members: Increase to 2.5-3 litres drinking water per person. Dehydration in older adults develops faster and has more serious consequences. Medication requirements may also add to the water budget.

Pets: Dogs require approximately 30ml per kilogram of body weight per day. A 20kg dog needs 600ml. Cats require approximately 250ml per day. Factor your pets into the calculation: they cannot be ignored in an emergency.

Hot climate or summer storage: In temperatures above 30°C, increase the drinking water budget by 50%. Heat-related dehydration is fast-moving and dangerous. This is particularly relevant for US readers in southern and western states.

What About Toilet Flushing?

Modern toilets use 6-9 litres per flush. A family of four flushing four times per day each uses 96-144 litres per day: four to six times the total drinking and hygiene budget.

You cannot store enough water to flush toilets normally during an extended outage. What you can do:

Short outage (under 3 days): Fill the bathtub before the outage starts if you have warning. A standard bathtub holds 150-200 litres: enough for approximately two days of flushing for a family of four. A WaterBOB bladder (100 gallons) gives enough flushing water for four to five days.

Extended outage: Reduce flushing frequency ("if it's yellow, let it mellow"), use a bucket-flush method with grey water from cooking or washing up, or use chemical toilet options. Maintaining drinking and hygiene water takes absolute priority over toilet flushing.

Practical Container Maths

The most common home water storage containers:

For a 72-hour minimum: fill 15 two-litre bottles, or 6 five-litre jugs, or buy three 25-litre containers.

For the two-week target: fourteen 25-litre containers (or two 55-gallon drums) is the most practical configuration for most homes.

The water storage guide covers the specific containers Kate recommends, how to treat stored water to extend its shelf life, and the annual rotation protocol she actually uses.

The One Mistake Everyone Makes

The most common water storage mistake is not the calculation: it is buying water and then forgetting about it.

Stored tap water without additional treatment has a shelf life of approximately 6-12 months in sealed containers. After that, it should be refreshed. If you store 75 litres of water in January and then forget about it, by December you have water that is technically safe but has been sitting in plastic for a year in a potentially warm space.

The solution is a rotation schedule: a fixed date each year when you drain, inspect, and refill your containers. Write it on the containers. Put it in the calendar. The water that you drain can go on the garden, down the drain, or into the washing machine.

Do not let perfect be the enemy of good. 75 litres of slightly-old water that has been stored correctly is enormously better than nothing. But do maintain your supply.

Related Guides

For containers, treatment methods, and rotation schedules: How to Store Water Long-Term.

For what to do if your stored water runs out or the source is uncertain: Water Purification Methods.

Frequently Asked Questions

Is one gallon per person per day enough?

One gallon (3.78 litres) per person per day is the FEMA minimum recommendation for the US. Kate's practical figure is 1.5 gallons (6 litres) per person per day, which allows for adequate cooking and hygiene rather than just survival-level hydration. One gallon is the starting minimum; 1.5 gallons is the realistic target.

How long can you survive without water?

In normal temperate conditions, three to five days without any water. In heat or with physical exertion, this drops to one to two days. Dehydration affects cognitive function long before it becomes life-threatening: at 2% body weight water loss (approximately 1.4 litres for an adult), decision-making ability is measurably impaired. The point of water storage is to not reach this state.

Does the calculation change for UK vs US households?

The physiology is the same. The planning context differs slightly. UK emergencies are more commonly flooding and power cuts (water supply usually maintained). US emergencies include wider scenarios including hurricane preparation, where 2+ weeks of self-sufficiency is more realistic. The core calculation (6 litres per person per day) applies in both contexts. US readers should add a buffer for hot climate storage and summer heat.