I asked my Doctor why do I and other people urinate so much at night time. Answer from my Cardiac Doctor = Gravity holds water in the lower part of your body when you are upright (legs swell). When you lie down and the lower body (legs and etc) is level with the kidneys it is then that the kidneys remove the water because it is easier. This then ties in with the last statement!
I knew you need your minimum water to help flush the toxins out of your body, but this was news to me. Drinking water at a certain time maximizes its effectiveness on the body:
2 glasses of water after waking up - helps activate internal organs
1 glass of water 30 minutes before a meal - helps digestion
1 glass of water before taking a bath - helps lower blood pressure
1 glass of water before going to bed - avoids stroke or heart attack
My Physician told me that water at bed time will also help prevent night time leg cramps. Your leg muscles are seeking hydration when they cramp and wake you up with a Charlie Horse.