Basically there is a set volume of water in your body, but this water gets used up by the processes of your body and when you exercise etc. This is why we need to drink, to top our level up. If you drink lots, you body can’t store all that excess water and it doesn’t need to. So it has to get removed somehow.
The organs that regulate how much water is in your body are yor kidneys. The job of your kidneys is to:
– Regulate the composition of your blood.
– Keep the volume of water in your body constant.
– Remove wastes from your body.
– Keep the pH of your blood constant (pH 7.4)
– Regulate your blood pressure.
– Maintain levels of calcium, sodium and potassium.
That’s a lot of work! Your kidneys basically filter your blood: the good stuff they put back in and and waste gets sent to your bladder. You need to drink lots of water because it helps your kidneys cleanse your blood, and if yuo didn’t your pee would be highly concentrated with all these acids and waste products and probably painful, so it’s better to drink plenty and dilute it down.