ABSTRACT
Any reduction from ‘normal’ body water content (euhydration) to a water deficit (hypohydration) is termed dehydration and can lead to dramatically reduced human performance and death. In any human thermal environment there are water requirements and a programme of drinking is required to preserve balance. The evaporation of sweat from the skin cools the body and plays an active role in human thermoregulation. Together with water loss due to insensible perspiration, moisture from breathing and that in urine and faeces (as well as other avenues such as tears or loss through injury) there can be a significant water and electrolyte loss from the body. Water provides the medium in which biochemical reactions occur and for the transportation of materials. From a state of euhydration the body achieves water balance if water inputs (by drinking) equal water outputs (sweat, urine, etc.). This is a continuous and dynamic process and there is an active controlling system to stimulate water intake, retention, secretion and excretion as well as its appropriate distribution around the body.
