Do you really need eight glasses of water every day? Should you filter your tap water? Get answers to these questions and more -- including if vitamin-spiked water is worth it.
The Institute of Medicine says adult men need about 13 cups (3 liters) per day of fluid; adult women need about 9 cups (2.2 liters) of fluid. (You get about an additional 2 1/2 cups of fluid from foods.)
"But one size doesn't fit all," says Leslie Bonci, R.D., C.S.S.D., director of sports nutrition at the Center for Sports Medicine at the University of Pittsburgh Medical Center and dietitian for the Pittsburgh Steelers. Your size and activity level affect your fluid requirements. Simply put, the larger and more active you are, the more you'll need.
"The easiest thing that anybody could do on a daily basis is monitor their urine color," says Douglas Casa, Ph.D., A.T.C., who studies hydration at the University of Connecticut. "Lighter urine color -- like lemonade -- means you're generally well-hydrated. If it's darker, like apple juice, you are most likely dehydrated."
Older adults' fluid needs don't change, but they're more likely to become dehydrated because their sense of thirst declines. Pregnant women and nursing mothers need slightly more water. Some medications, such as antihistamines and certain antidepressants, increase your fluid needs too.
Yes, in hot weather you typically need to drink more because you sweat more, especially if you're exercising. Humidity also increases your water needs. When it's humid and warm -- a double whammy -- you may need as much as two times more water than when it's drier.
And although we tend to skimp on water when it's chilly out -- don't. You also lose more water while breathing frigid, dry air. Fluid needs don't change at altitude (11,500 to 17,500 feet): in fact, your body finds a new normal at 2 percent dehydrated and actually functions better.
Sodium, potassium, chloride, calcium and magnesium are essential for vital reactions in your body -- all are electrolytes and all are lost in sweat. It's important that the concentration of those electrolytes doesn't get too high or low -- and that they are replaced when depleted. If your electrolyte balances are out of whack, you won't properly absorb the water you do drink. Most electrolytes can be replenished simply with regular, healthy meals.
"If you're well-nourished and well-hydrated, then exercise can be at least an hour in length before you need to concern yourself with including electrolytes in the beverage," says Cheuvront. Replenishing what you lost could be as simple as having a few pretzels. You could also try a sports drink, since they often contain sodium. For a walk in cool weather or a short run, water will suffice. (
