when you drink water...

[SKA]

how long does it take to go through the the whole body and leave?

[lafrancaise]

It depends on what's getting digested in your stomach and if your body needed the water to dehydrate itself. If the body needs all the water it won't 'leave'

[Grunty]

lafrancaise is right, but I know a nurse who looks after people who are quite helpless. They are not involved in strenuous exercise, and just sit in their chairs. She says it is about 25 minutes until they wet themselves. Sorry, but you did ask.

[sheamus]

You also need to take into account the size of a persons bladder and the strength of their stomach muscles. Old people will often pee sooner because their stomach muscles are weaker (apparently)...