Human Nutrition If the importance of a nutrient is judged by how
long we can do without it, water ranks as the most important. A
person can survive only eight to ten days without water, whereas
it takes weeks or even months to die from a lack of food. Water
circulates through our blood and lymphatic system, transporting
oxygen and nutrients to cells and removing wastes through urine
and sweat. Water also maintains the natural balance between
dissolved salts and water inside and outside of cells. Our
joints and soft tissues depend on the cushioning that water
provides for them. While water has no caloric value and
therefore is not an energy source, without it in our diets we
could not digest or absorb the foods we eat or eliminate the
body's digestive waste. The human body is 65 percent water, and
it takes an average of eight to ten cups to replenish the water
our bodies lose each day. How much water a person needs depends
largely on the volume of urine and sweat lost daily, and water
needs are increased if a