ObesityHelp

You can do a test on yourself. 

Weigh yourself before a one hour workout.  Do the workout without drinking anything.  At the end weigh yourself again (preferably naked both times)  you will find out how much you have lost for the conditions of the workout (temp, intensity, humidity) in one hour. 

You can take a liter with you and drink that 30 minutes after the workout. I do not drink immediately or eat. Yes, weighing before and after may help but that wouldn't be noticed in an ordinary scale.