It can save you from being dehydrated. For survival, you'll die for 21 days or more. Like many living things, you need water for the human body to stay alive and healthy. So again, your body uses water in all its cells, organs, and tissues to help regulate its temperature and maintain other bodily functions. Because your body loses water through breathing, sweating, and digestion, it's important to rehydrate by drinking fluids and eating foods that contain water.