Fruit consumption wadds to daily liquid intake. - Rudolph Brown/Chief Photographer

R.J. Ignelzi, Contributor

The long-held recommendation to drink at least eight glasses of water a day (in addition to other fluids we down) is all wet, medical experts say.

"It's an old wives' tale that we need to drink eight glasses of water each day," says Dr. Kenneth Roth, an internal medicine physician at Sharp Community Medical Group in San Diego. "Hydration is good for you, but you have to drink appropriately."

How much fluid we need varies among individuals depending on age, general health, how long and how intensely you exercise, what foods you eat, what medications you take and how much you sweat. Straying too far from your hydration limits can have devastating effects. Too little water means dehydration and your organs shut down. Too much water and you can experience hyponatremia or water intoxication. Your blood becomes diluted, your brain swells and coma or death can follow, as demonstrated recently by a California woman who died after participating in a radio station's water-drinking contest.

Milk counts

In 2004, after reviewing more than 400 studies, the National Academy of Sciences' Institute of Medicine rejected conventional hydration wisdom. It concluded that most men need about 15.5 cups of fluid a day and women about 11.5 cups. Before you feel compelled to chug another glass of water, be aware that this recommendation includes fluids from all beverages and foods, including the milk on your cereal, the two cups of coffee you had this morning, the juicy orange you ate as a snack and the chicken noodle soup you had for lunch.

The academy said the majority of Americans already get that much liquid in their everyday diets. But, just because we don't need to guzzle as much water as once believed doesn't mean we should be running on empty.

"The idea of drinking water is really essential to maintain normal good health," says Dr. James Dunford, emergency room physician with University of California San Diego Medical Center and medical director of San Diego's EMS system. "Water is needed to help preserve body functions and vital organs and maintain blood pressure. It brings nutrients to the cells and washes away the toxins. Water is the most important molecule we commonly take for granted."

Even mild dehydration, a loss of just one to two per cent of body weight, can produce symptoms including weakness, dizziness, fatigue, headache, and reduction in mental and physical performance. If dehydration continues, your body may not have enough water to dissipate heat through sweating, which can result in heat stroke and even death. "Many more people are still not properly hydrated than overly hydrated," says Cedric Bryant, chief exercise physiologist for the American Council on Exercise. "Just because of what happened with the (Sacramento woman in the radio contest), we don't want people to have an unnecessary fear of fluid consumption."

Listen up

Listening to your own body is the best way to gauge your hydration needs, doctors say. When you're thirsty and seem to be sweating buckets after a long period of exercise or being outside on a summer afternoon, drink. But, if you're barely sweating and not thirsty, skip the frequent water breaks.

However, sometimes certain people need to give special attention to fluid intake. The elderly may need to monitor their fluids more closely, because the sense of thirst tends to diminish with age. And, when illness causes fever, diarrhoea or vomiting, extra fluids supplemented with electrolytes are needed to replace those lost essential body salts. Electrolytes, such as sodium and potassium chloride, control the movement of water in and out of the cells of the muscles and organs.

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