The function of urine
The body is made up of 60% water, but during the day we lose a proportion of it by sweating, breathing out and by urinating. To compensate for all this loss of liquids, it is important to drink.
How much we need to drink depends upon one's size and the activities we perform.
An adult should drink roughly 2 litres of liquid a day (depending on levels of physical activity). The reason why we urinate is that, amongst other things, we need to get rid of liquid the body doesn't need. Urine is also an important part of the body's own 'self-cleaning' system.