Guide · Water

How much water you need

Knowing how much water you need helps you plan, ration sensibly and spot trouble early. Most people need more than they think, especially when it's hot or they're working hard.

Everyday amounts

• Resting in mild weather: about 2 to 3 litres a day for an adult, including what you get from food.
• Walking, carrying loads or working: 4 litres or more.
• Hot weather or heavy effort: 6 litres or more. You can lose over a litre an hour through sweat.
• Cold weather: still around 3 litres or more. Cold air is dry, and you lose a lot of water through breathing. People often forget to drink because they don't feel thirsty.

Children, pregnant or breastfeeding women, people who are ill and older adults need extra attention. Older people and young children may not notice or say that they're thirsty.

For planning and storage

Plan for about 3 litres per person per day for drinking and simple cooking. If you're storing water at home, allow around 4 litres per person per day so there's some for basic washing too. Don't forget pets.

Ration sweat, not water

If water is limited, don't try to make it last by drinking almost nothing. Dehydration will slow you down, cloud your judgement and can become dangerous within a day or two in the heat. It's better to drink what your body needs and reduce how much you lose:

1. Rest in the shade during the hottest part of the day.
2. Do hard work in the cool of early morning or evening.
3. Keep your clothes on — loose, light-coloured layers and a hat slow evaporation.
4. Breathe through your nose and talk less.
5. Avoid alcohol and caffeine-heavy drinks.
6. Eat less if water is very short, especially salty or high-protein food, as digesting it uses water.

Drink little and often

Sipping regularly is better than drinking a lot at once. Your body absorbs it more steadily and less passes straight through.

Check yourself

Your urine is a useful guide. Pale straw colour means you're drinking enough. Dark yellow, strong-smelling or very little urine means you need more. Some vitamins and foods change urine colour, so look at the amount as well.

Don't overdo it either

Drinking huge amounts of plain water during long, sweaty exertion, without eating anything salty, can dilute the salt in your blood. This is rare but serious. Drink to thirst and eat normally, or add a pinch of salt or a rehydration sachet if you're sweating heavily for hours.

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