We need about 2,5 litres a day. If water intake and elimination are balanced, the water level in the body is stable. To maintain this stability we need to drink at least 1 litre a day. It is recommended however to drink 1,5 to 2,5 litres a day to prevent dehydration and the circulatory weakness that results and to flush harmful agents from the body before they accumulate in the joints, for example. The daily fluid requirement depends on height, weight and climatic conditions. In the case of exertion resulting in perspiration or high heat the requirement is several times higher. A professional tennis player can lose up to 8 litres in a single match.

About half of the fluid intake requirement is satisfied in the form of drinks, about 40% in food and the rest is produced by the body's metabolism. Melons, iceberg lettuce and courgettes contain more than 90% water. Water is also present in many other food items that at first glance don't appear watery. Spaghetti is 65% water, and the level in bread is 30%.