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