All known forms of life depend on water. Up to 70% of a human's body weight is water - that needs to be topped-up regularly for us to stay healthy.
Without some source of water we die very quickly. We can last a few days at most, and we may only last a few hours.
Humans lose water from their bodies all the time, mostly through urine and sweat. We use a lot of water when we turn our food into energy. Water is also lost as vapour from our lungs when we breathe. All this must be replaced with liquid from our food and drink.
How much water is enough?
To work well, our bodies need between one and seven litres of water per day. Exactly how much you need will depend on how much physical exercise you do and other factors such as temperature (if it's a hot day you will need more water).
Not getting enough water leaves you dehydrated. This can cause headaches, tiredness and loss of concentration. Staying dehydrated for a long time can cause lots of health problems, for example damage to your kidneys.
Tips for getting enough water
Here's some advice to help you get enough water each day:
- Have a glass of water when you wake up
- If you're out and about during the day, carry a bottle of water so you can have a drink whenever you want
- Eat more fresh fruit and vegetables- they contain a lot of water