Why do you have to drink sooo much water in order to lose weight?

Hydration is VIP. It takes more water to burn fat than it does to burn protein or carb. If your body is even slightly dehydrated you will derail fat burning and burn the other "fuels" instead. Most of us are slightly dehydrated anyway so it seem to take a lot of water - some to get you adequately hydrated and then more to burn fat.