Why do we need water?

Water comprises 50 to 70 per cent of an adult's total body weight, and without regular top-ups, our body's survival time is limited to a matter of hours or days.
Water is lost from the body through urine and sweat, and must be replaced through our diets. Many people, though, don't consume enough and as a result may become dehydrated, causing symptoms such as headaches, tiredness and loss of concentration. Chronic dehydration can contribute to a number of health problems, such as constipation and kidney stones.
How much do we need?
The body gets its water from three sources:
1)From drinks, either plain water or as part of other beverages.
2)From solid foods, especially fruits and vegetables.
3)As a by-product of chemical reactions within the body.
The British Dietetic Association advises that the average adult should consume 2.5 litres of water per day. Of this, 1.8 litres - the equivalent of six to seven glasses of water per day - must be obtained directly from beverages. This should be increased during periods of hot weather or during and after periods of physical activity.
Water is the major ingredient of all drinks: carbonated and still drinks are 65 per cent water, diluted squashes are 86 per cent water (after dilution) and fruit juices are 90 per cent water. But drinking plain water is still the most effective way of replacing lost fluids.