Water makes up 85 percent of our blood, 80 percent of our muscles, and 75 percent of our brains. It regulates body temperature, transports nutrients, and removes impurities. We can't survive without it.
It comes in seemingly endless variations—tap, bottled, bubbly, lightly sweetened, fruit-flavored, mineral-fortified, and electrolyte-enhanced. We also obtain it in the many other beverages we drink, such as juices, colas, teas, and coffees, not to mention various foods.
But how much fluid do you need, what are the best sources, and what special considerations are important for exercisers?
"There are so many misconceptions, such as the old adage about drinking eight eight-ounce glasses of water per day," says Samuel N. Cheuvront, PhD, RD, principal investigator with the U.S. Army Research Institute of Environmental Medicine in Natick, Massachusetts.
To help clear up the confusion, we turned to the experts for answers that hold water.
How much fluid do I need each day? Optimal hydration varies depending on activity level, body size, sweat rate, and climate. Because of that, the Institute of Medicine, the group that provides scientific research to formulate public health policies, such as the U.S. dietary guidelines, recommends an Adequate Intake (AI) rather than a specific daily amount.
AI is a more flexible measure; a strict recommendation does not account for individual needs. For a sedentary woman living in a moderate climate, the AI is 2.7 liters or 91 ounces of fluid a day. A man's AI is 3.7 liters or 125 ounces of fluid per day.
Is drinking water the only hydration option? To stay hydrated, you can consume any beverage, including milk, juice, soda, and even coffee and tea (their diuretic role has been exaggerated). Also, food helps you meet daily fluid needs. "Soup, fruit, vegetables, and dairy products are all more than 80 percent water," says Roberta Anding, MS, RD, a clinical dietitian at Baylor College of Medicine in Houston and spokesperson for the American Dietetic Association. For example, a typical wedge of watermelon contains approximately 9 ounces of water. Food also helps the body hold on to fluids because of the electrolytes it contains—minerals like sodium, potassium, and chloride that bind with water. Drinking beverages with meals and snacks helps your body retain water longer.
If I only drink when I'm thirsty, will I consume enough? "Generally, yes," Cheuvront says. We often hear that thirst is a poor indicator of hydration, but this advice really only applies to endurance athletes, people who work outdoors in hot climates, or those who may risk dehydration due to illness. For sedentary and moderately active people, thirst is a good guide. According to the U.S. Department of Agriculture, the combination of thirst and usual drinking behavior, especially the consumption of fluids with meals, is sufficient to maintain normal hydration.
