I do the same - for two reasons!
Firstly, I go from work to WI, via picking up my hubby. So it's an hour from when I finish work to when I get to my CDC, so if I didn't stop drinking water an hour before finishing work, I'd be busting to go on the journey!
But, I also believe it does make you weigh heavier, I have always been the same whatever diet I do - it's probably nonsense really, but I still do it! x