So, I was wrong.

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, according to a new report from the Institute of Medicine, the group that sets desirable levels of nutrient intake for Americans of all ages.

The report, issued last week, reviewed the status of water, salt and potassium consumption by Americans and Canadians and set desirable intake levels for these nutrients.

Healthful Drinking

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.

Dr. Lawrence Appel of the 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.

Although caffeine, as a diuretic, increases the excretion of urine, it does not lead to a deficiency of body water, the panel concluded, suggesting that the effect is fleeting.

Furthermore, Dr. Appel said, ''People get adequate amounts of water from normal drinking behavior -- consumption of beverages at meals and in other social situations -- and by letting their thirst guide them.''

Will this curb the explosive growth of specialty waters? Probably not. But it should be reassuring news for millions of people who worry that they do not drink enough.

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.

How can you tell if you are getting enough water? Clearly, if you are thirsty, you need to drink more. Likewise, if your skin is shriveled, if you are prone to muscle cramps or if you are chronically constipated, chances are you are not drinking enough.

There is no harm in drinking more water than recommended, as long as you do not go overboard on it. Athletes who drink too much water without also replacing the salts lost in sweat, for example, can have health problems like abnormal heart rhythms.

On the other hand, drinking more water may help curb runaway obesity. Every good weight-loss program recommends drinking a glass of water (or an equivalent beverage) before and with every meal, since it both fills you up and improves digestion.

Too Much Salt

The panel, formed under an arm of the National Academy of Sciences, found that Americans typically consume far too much sodium chloride, or salt. In some cases, the consumption runs as high as three times the amount needed for good health, or even higher.

The average man takes in 7.8 grams to 11.8 grams of salt each day, and the average woman consumes 5.8 to 7.8 grams, figures that the panel regards as underestimates because they do not include salt added at the table.

How much salt should people eat? For healthy adults 19 to 50, the desirable level is 3.8 grams of salt (about two-thirds of a teaspoon, or 1,500 milligrams of sodium) daily, the amount needed to replace what is lost in sweat.

For an upper limit, the panel set 5.8 grams of salt a day (a little more than one teaspoon), but noted that this was not a desirable amount. The panel said that more than 95 percent of American men and 75 percent of American women ages 31 to 50 regularly consumed salt in excess of the upper limit established by the group.

Consuming too much salt, which means too much sodium, increases the risk of developing high blood pressure, which can in turn lead to strokes, heart attacks and kidney disease. Blood pressure tends to rise in direct relationship to the amount of sodium a person consumes.

Some people are especially sensitive to the harmful effects of salt, including the elderly, African-Americans and people with chronic diseases like hypertension, diabetes and kidney disease, the panel noted.

An appetite for salt is an acquired taste, since anthropological evidence strongly suggests that humans evolved on a diet low in sodium and rich in potassium.

Our vegetarian ancestors consumed less than a gram of salt a day and even heavy meat eaters took in only about 4 grams on good hunting days.

Currently, more than three-fourths of the salt in the American and Canadian diets comes from prepared and processed convenience foods, including those bought from vending machines, snack bars and restaurants.

Enough sodium is naturally present in foods and beverages to meet the body's need for it. Only those who labor or exercise strenuously for long periods in hot weather are likely to need more sodium than a natural diet provides.

Thus, anyone who loses six or more pounds in a workout should replace some of the lost salt, along with water.

When it comes to sodium and potassium, modern food producers and vendors have sabotaged our natural metabolic processes.

Since we evolved in a low-sodium environment, our bodies are designed to hang on to however much sodium they can get.

But since potassium was plentiful in the early human diet, evolution built in a mechanism for releasing potassium to protect against a hazardous excess, which can cause abnormal heart rhythms and muscular paralysis.

Potassium Problems

Now, we consume far too few of the potassium-rich foods, which can help to lower blood pressure, blunt the effects of salt and reduce the risk of kidney stones and bone loss.

The panel recommended daily consumption of 4.7 grams of potassium a day for adults, but noted that American women 31 to 50 consumed no more than half this amount, and that men didn't do much better.

The panel also noted that African-Americans, who have a higher rate of hypertension and thus may benefit most from more potassium, generally consumed less potassium than non-Hispanic whites.

People taking diuretics to control high blood pressure or edema are especially at risk of developing a potassium deficiency.

Among the best dietary sources of potassium, on a per calorie basis, are spinach, cantaloupe, almonds, brussels sprouts, mushrooms, bananas, oranges and orange juice, grapefruits and potatoes, the panel said.

Other good sources include dried fruits, peanut butter, bran, meats, dried beans, peas, coffee, tea and cocoa.

If you can handle the sugar, sports drinks are also good sources of potassium.

Drawing (Drawing by Toni Zules)