An interesting page on where we can find our water daily but the statistics seem maximized a bit: http://www.angelamorelli.com/water/
Nonetheless, a pretty cool read. As for why we don't seem to urinate as much as we drink is accounted to many reasons, loyal to da game named a few.
You use a lot of water in your body, it's necessary for life functions. A lot of people actually don't drink as much as they are supposed to, which is around 2-3 litres a day.
Estimates are around 40-50% of people are actually dehydrated, without them actually knowing. :/