Water is one of six categories of nutrients that the body acquires from food. The others are protein, carbohydrates, fat, fibers, vitamins and minerals. Of all these nutrients, lack of water is the most immediate concern for survival because dehydration can become life threatening in a matter of days.
Water is vital for nearly all bodily functions. As the main component of blood, it is necessary for the transportation of oxygen and nutrients around the body. It helps regulate body temperature and is a part of saliva and other digestive enzymes. It is involved in most of the body's biochemical reactions. The human body is mostly water and cannot survive without it.