<P> The human body contains from 55% to 78% water, depending on body size . To function properly, the body requires between one and seven liters of water per day to avoid dehydration; the precise amount depends on the level of activity, temperature, humidity, and other factors . Most of this is ingested through foods or beverages other than drinking straight water . It is not clear how much water intake is needed by healthy people, though most specialists agree that approximately 2 liters (6 to 7 glasses) of water daily is the minimum to maintain proper hydration . Medical literature favors a lower consumption, typically 1 liter of water for an average male, excluding extra requirements due to fluid loss from exercise or warm weather . </P> <P> For those who have healthy kidneys, it is rather difficult to drink too much water, but (especially in warm humid weather and while exercising) it is dangerous to drink too little . People can drink far more water than necessary while exercising, however, putting them at risk of water intoxication (hyperhydration), which can be fatal . The popular claim that "a person should consume eight glasses of water per day" seems to have no real basis in science . Studies have shown that extra water intake, especially up to 500 ml at mealtime was conducive to weight loss . Adequate fluid intake is helpful in preventing constipation . </P> <P> An original recommendation for water intake in 1945 by the Food and Nutrition Board of the United States National Research Council read: "An ordinary standard for diverse persons is 1 milliliter for each calorie of food . Most of this quantity is contained in prepared foods ." The latest dietary reference intake report by the United States National Research Council in general recommended, based on the median total water intake from US survey data (including food sources): 3.7 liters for men and 2.7 liters of water total for women, noting that water contained in food provided approximately 19% of total water intake in the survey . </P> <P> Specifically, pregnant and breastfeeding women need additional fluids to stay hydrated . The Institute of Medicine (US) recommends that, on average, men consume 3.0 liters and women 2.2 liters; pregnant women should increase intake to 2.4 liters (10 cups) and breastfeeding women should get 3 liters (12 cups), since an especially large amount of fluid is lost during nursing . Also noted is that normally, about 20% of water intake comes from food, while the rest comes from drinking water and beverages (caffeinated included). Water is excreted from the body in multiple forms; through urine and feces, through sweating, and by exhalation of water vapor in the breath . With physical exertion and heat exposure, water loss will increase and daily fluid needs may increase as well . </P>

Describe the following properties of water and explain how each is important to living things