The majority of an adult's body weight is composed of water found in its body fluids, accounting for 55 to 60 percent of an adult's total body weight. As a result, water is the most vital nutrient. Because of water's essential roles in so many of the body's functions and reactions, adults, in general, can survive without any water for up to ten days in moderate weather conditions. This is in sharp contrast to being able to live without any food for about eight weeks. According to the Committee on Dietary Allowances, most people, in general, need at least six to eight 8-ounce glasses of water or other fluids daily.
Illness affects a person's water requirement as well.