You're going to lose some water weight no matter how hydrated you stay. Carbs soak up water, so without carbs you will weigh less as the water disappears. You

You're going to lose some water weight no matter how hydrated you stay. Carbs soak up water, so without carbs you will weigh less as the water disappears. You don't want to be dehydrated, but especially if you're fasting, you can overdo it on the water and end up in the opposite arena: overhydrated. This can suck out minerals and nutrients from your body, and since you're not eating to replace them, you're in major trouble.