So how much water does a man really need?

You may not have to drink eight glasses of water a day to be well hydrated, and you can count caffeinated beverages in your total water intake. That's the finding of the Washington-based Institute of Medicine, the group that sets desirable levels of nutrient intake for Americans of all ages.

It has reviewed the status of water, salt and potassium consumption by Americans and Canadians and set desirable intake levels for these nutrients. The panel found that women who appeared to be adequately hydrated consumed the equivalent of about 2.7 litres of fluids each day, and men about 3.7 litres.

Dr Lawrence Appel, of Johns Hopkins University, who headed the panel, explained: "While drinking water is a frequent choice for hydration, people also get water from juice, milk, coffee, tea, soda, fruits, vegetables and other foods and beverages, as well."

No mention was made of alcohol, however, which increases the body's water needs. "People get adequate amounts of water . . . by letting their thirst guide them," Dr Appel said, informs &to=http://www.smh.com.au' target=_blank>SMH.com.au

According to &to=http://www.boston.com' target=_blank>Boston.com a panel of some of the most esteemed nutrition and health experts in the United States and Canada said there's no need to try to get eight glasses a day: People should just drink when they're thirsty.

American women already average 9 cups of water a day from all beverages combined, and American men, 13 cups, said the panel, which was convened by the Institute of Medicine, a nonprofit group that provides health policy advice to the National Academy of Sciences. That's enough, the panel concluded, when you throw in the 2 to 3 extra cups of fluid contributed by the moisture content of the foods we eat. Consider that a turkey sandwich made with Swiss cheese, lettuce, and tomato on whole-wheat bread contains almost a half-cup of water; a tossed salad with vinaigrette dressing, close to a full cup.

The panel also said it is a myth that coffee and alcoholic beverages are dehydrating (although the bottled water association, on its website, continues to argue they are). "Caffeinated beverages contribute to daily total water intake, similarly to noncaffeinated beverages," said Michael N.

So how did the eight-glasses-of-water-a-day myth get started in the first place? "That's a good question," Sawka said. It certainly "evolved based on something not having anything to do with scientific evidence."

The expert panel that prepared the report found that women who appeared to be adequately hydrated consumed the equivalent of about 91 ounces of fluids each day, and men about 125 ounces. That is actually more than eight glasses (64 ounces). But only 80 percent of it came from drinking water; the rest came from other beverages, and from foods.

While the institute used the recommended levels of 91 ounces for women and 125 for men, if they are healthy, it noted that the need for water increased significantly with strenuous or prolonged physical activity and for those who live in hot climates. Some may require twice the amount of water adequate for a sedentary person at moderate temperatures or even more.