Your body needs water to live.
When digesting and processing food your body absorbs more water to work better.
Think of it as the oil for your car. If you don't have any in you and you chuck in a heap of food, expecting it to work over-time and quickly well that is like having no oil in your car and driving to Brisbane from Sydney. VERY F%^*EN STUPID!
Just a good diet and exercise regime will speed up your metabolism.
If you want to help burn extra calories, then there are little tricks, e.g.
-drink really cold water - your body burns more trying to digest it as opposed to room temperature water.
-eat celeray, paw paw, pineapple etc - healthy foods that burn more calories when digesting them than they give you.
There is a whole bunch of them out there. But they all add just little bits. The main thing is eating, sleeping and exercising right.