Well, on such a vlcd you need to keep yourself hydrated as you arent eating much, so thats one thing - to stop yourself from getting dehydrated - but you already knew that...
And number two, you need to drink to flush out all of the toxins and the ketones, if you dont drink, where's all the weight gonna go?
I always say the more you drink the more weight you lose as the more you go to the toilet the more you are flushing away.....
Hard though isnt it, so rank sometimes i get bored of it!