There was a program on TV about a year back in which a pair of twins were studied for one solid week. Before the study, they both drank 500ml of water a day, no other drinks at all.
During the study, one of the twins was to consume 8 glasses of water a day (2 UK litres, I assume, since I can't remember the exact size of the glasses) whilst the other twin remained on their normal 500ml.
Prior to and at the end of the study, measurements were taken concerning hydration of skin, hair (I think), skin elasticity, and a host of other fluid related readings; there was no difference in the repsonse of either twins' body at the end of the study and the twin that was drinking more did not have any higher a hydration level in the skin than the twin that was on her normal 500ml of water a day.
36.5 kg /80.3 lb Middle-Finger DL (right hand)...