We will die because while we need food primarily for strength, we need water for multiple body functions. The adult body is made of 67% water. As such water is needed to maintain many body functions. Water lubricates joints, helps to control body temperature through sweating and respiration and also helps to flush waste from the body. It is a key ingredient in all fluids in the body. The human body can go about three weeks without food but can only go at most a week without water. This is because in difficult times, the body begins to consume fat and muscle to stay alive. But there is no such reservoir for water. As such water is very important. More so even than food