06/30/2011 03:06 pm ET | Updated Aug 30, 2011

Summer Hydration Mysteries Solved

With the Fourth of July just days away, it's official: Summer is in full-swing.

For many, the upcoming weekend represents a welcome opportunity to flee the cube and bask in the sun, but how to do so without harming your health?

Much has been made of the need to slather on sunscreen to protect against UV rays, however, hydration is another critical element of summertime health. Dehydration can range from the mild -- often marked by symptoms like a dry, sticky mouth -- to the severe, or even life threatening. Fortunately, experts agree that normal, healthy adults and children can follow a few simple rules to stay safe.

Do You Really Need Eight Glasses Of Water A Day?

In 2002, Dartmouth Medical School physician Dr. Heinz Valtin set out to examine the roots behind the popular "drink eight glasses of water a day" maxim.

The subsequent review, which was published in the American Journal of Physiology, concluded there were no scientific studies supporting that rule. In an e-mail to The HuffPost, Valtin wrote that to date, no one has presented him with new data that suggests otherwise.

Which raises the question: How much water do people really require?

"In general, you need about 1 mL of water for every calorie you take in," said Dr. Stanely Goldfarb, a professor of medicine at the University of Pennsylvania, who researches fluid and electrolyte management. "So someone who eats around 2,500 calories per day should have about 2.5 to 3 liters of water per day."

If that's too specific for you to actually monitor, he suggests that people are generally fine letting their thirst be their guide. And Valtin agrees.

"For healthy adults in a temperate climate leading a largely sedentary existence, my advice is 'drink what you customarily do at and between meals, plus when you are thirsty,'" he said.

Does Coffee Count As A Beverage?

In a word, yes.

"Our total fluid intake not only comes from drinking water and other beverages such as tea and coffee, but also from the foods we eat," said Toby Smithson, R.D., a national spokesperson for the American Dietetic Association.

Even though research suggests that caffeine is a mild diuretic, Smithson said that a 150 pound adult can drink up to 32 ounces, or four cups of brewed coffee per day, and still maintain his or her hydration status.

Should You Pre-Hydrate?

The experts are ever-so-slightly divided on this one.

Smithson says that by the time you are actually thirsty, you may have lost 1 to 2 percent of your body weight in water.

But Goldfarb says that thirst is a perfectly good marker of when you should drink, adding the caveat that this may not be true in older adults who may have lost their sense of thirst.

Groups that counsel on hydration offer similar advice.

The International Marathon Medical Directors Association changed its hydration guidelines in 2006 to state that "thirst will actually protect athletes from the hazards of both over- and under-drinking," meaning it is more in the Goldfarb camp. While The American College of Sports Medicine includes in its guidelines a section on how drinking before exercise -- "if needed" -- should be done to start the body at normal fluid and electrolyte levels.

So What About Athletes?

Athletes and people who plan to head outdoors to exercise, whether it's taking a jog or doing yard work, do need to be more aware of hydration, given that they are more likely to lose fluids through perspiration.

"When you're working out, your muscles are generating heat, and the way the body gets rid of that is through sweating," explained Dr. Karen Reznik Dolins, a professor of nutrition and physical education at Columbia University. "If you're exercising, you're increasing your fluid output and someone who is physically active is going to need more fluids."

But just how much more can be tricky to determine.

Dollins suggested that elite athletes, or people who plan to work out hard, should consider weighing themselves before and after a workout to get a better sense of just how much fluid they've lost. She admitted, however, that few people do that.

Another easy test for both athletes and non-athletes alike? Look at the color of your urine. If it looks like lemonade, you are probably OK. If it looks more concentrated, like apple juice, you probably need more fluids.