Hi, many reasons might exist for you to have water fast. As the water has no energy and calorie it might be a useful method for reducing weight, having weight loss and it might be useful for removing toxin from body. Well but not all theories about water fast is correct and it is suggested to use a regular diet for being healthy and control your weight. When you have a fast weight loss the probability for back to the previous weight is a lot. And if you do exercise you can also lose weight. Anyway if you want to have water fast it can be suitable for you and this video can help you.