The importance of hydrationWater plays many important roles within the body. Water is the major part of most of the body's cells (except for fat cells) and it also cushions and lubricates the brain and the joints. It transports nutrients and carries waste away from the body cells. It also helps regulate body temperature by redistributing heat from active tissues to the skin and cooling the body through perspiration.
Water is the main constituent of the human body: it is normally about 60% of body weight in adult males, and is slightly lower, about 50-55%, in females due to their higher proportion of body fat. The muscles and the brain are about 75% water, the blood and the kidneys are about 81%, the liver is about 71%, the bones are about 22% and adipose tissue is about 20%.
Most of the water in the body is found within the cells of the body (about two thirds is in the intracellular space), and the rest is found in the extracellular space, which consists of the spaces between cells (the interstitial space) and the blood plasma.
Total body hydration and the balance between input and output of water are under homeostatic control by mechanisms which modify excretory pathways and stimulate intake (thirst).
The body requires water to survive and function properly. Humans cannot live without drinking for more than a few days - depending on weather, activity levels and other factors - whereas other nutrients may be neglected for weeks or months. Although commonly it is treated rather trivially, no other nutrient is more essential or is needed in such large amounts.