The eight-glass recommendation is based on the standard 2,000 calorie diet. The idea is that for every calorie burned, people should drink 1 milliliter of water. And 2,000 milliliters is the equivalent of eight cups, said Pauline Williams, a registered dietitian and professor of nutrition at Brigham Young University.
Everyone's calorie intake is different, so is his or her activity level, she said. Eight glasses of water might be appropriate for some people, but not for others.
The question is how much water is right for you?
The sweat test • The best way to know is to figure out how much you sweat. To determine your "sweat rate" simply weigh yourself before and after you exercise.
"Any loss during a workout is fluid," Beals said. "So, if I lose one pound I need to re-hydrate with 16 ounces of water."
Obviously it's not possible to be weighed every time you exercise, but you will see a pattern that can help you develop a hydration schedule, Beals said.
The sweat rule also applies when you are participating in outdoor activities such as hiking, running, mowing the lawn, gardening or even spending a day at an amusement park.
Basically, the rule of thumb is: the more you sweat, the more water you need. Some people naturally sweat more even when they are not exerting themselves. This group will need more liquid than those who sweat less, experts say.
And it is possible to over-hydrate, especially on a hot day, which decreases sodium levels in the blood. While drinking water, be sure to replenish with a little something salty, too.
Another way to track proper hydration is the color of your urine. It should be a light yellow.
If it's dark, you should be drinking more water, Beals said. Many people believe "that urine should be clear," she said. "But urine should never be clear.
Hydration is especially important for children. Parents should make sure that kids take beverage breaks whenever they are playing outside and under the hot sun.
"Remind kids to drink, because they'll be playing and they'll simply forget," Williams said. "Since they have smaller bodies, kids can be come dehydrated much sooner than adults."
More water, please • Symptoms of dehydration for kids can include extremely flushed cheeks, no urination and sunken eye sockets, she said. Adults may experience muscle cramps, nausea and vomiting and light-headedness.
Hydrating can include beverages and foods besides water. Juice, watermelon, milk and soup are a few examples. Even diuretics such as coffee and tea, provide some hydration.
"Their diuretic effect has been grossly overstated," Beals said. "[They do] make you urinate, but you probably retain more than half the fluid in a latte. Basically, anything that is fluid in nature is hydrating, within moderation."
That doesn't mean you can drink nothing but soda pop, Beals added, "but if that's part of your diet it absolutely does provide you with fluid."
If your goal is weight loss you should avoid soda, juice and sport drinks that are high in calories. Sports drinks were designed for elite athletes who need to replenish calories and electrolytes quickly, Beals said.
"Water is so good for you, and it's calorie free!" she said.
Whatever you may be drinking, staying properly hydrated is important, said physical therapist Sally Pfiffer. Muscles are 70 percent water, so you can feel tired and achy if you're dehydrated.
"To have them work right," she said, "you need to make sure you're drinking the right amounts of water."
Sweat test • Weigh yourself before and after you exercise and replace any fluids lost. For example, if you lost one pound during a workout, re-hydrate with an equal amount (16 ounces) of water.
Color test • Urine color should be light yellow. If it's darker, you need to be drinking more water. It should never be clear.
Child hydration • Parents should make sure that children take beverage breaks whenever they are playing outside. Their bodies are smaller and they can become dehydrated much faster than adults.
Calorie conundrum • If you're exercising to lose weight, avoid sports drinks as they are high in calories.
Advice • Consult a registered dietitian for more advice. More information also is available at www.eatingrightutah.org.