Water is more important than any other single compound to life. It is involved in several body functions. Water acts as a vehicle for transport of solutes. Water is the major body constituent. An adult human contains about 60% water (men 55–70%, women 45–60%). A 70kg man contains 42L of water. This is distributed in intracellular (inside the cells 28L) and extracellular (outside the cells 14L) compartments, respectively known as intracellular fluid and extracellular fluid. The body has tremendous capacity to regulate its water content. In a healthy individual, this is achieved by balancing the daily water intake and water output.