Diets come in all shapes and sizes. Some are complicated. A diet dependent on your blood type might seem overly complex compared to a diet, for example, that just requires you to cut out almost all carbs. On the other hand, an ultra-low-carb diet might seem incredibly convoluted compared to the grapefruit diet. That diet calls on you to eat grapefruit almost exclusively for a few days or weeks. However, all of these diets, regardless of their intricacy, are doomed to fail if you aren’t drinking enough water.