Water serves a vital role in the everyday operation of cells within the body. The maintenance
of water balance is essential for health and is determined by a sophisticated scheme that
balances water input (drinking) and water output (perspiration, urine) from the body. Specific
mechanisms interact to control thirst, drinking behavior, and the output water from the
kidney when the body is faced with a water deficit. However, restoring body water balance
following dehydration ultimately depends on mechanisms that regulate fluid intake or
drinking. Despite these sophisticated defense mechanisms, the restoration of water balance
following dehydration is usually slow and incomplete; a problem termed “involuntary
dehydration.” Thus, even healthy young adults should be advised of the benefits of complete
water replacement following dehydration