You want to go into your workout properly hydrated, and drink enough during to keep your body running smoothly. Afterward, it's all about replenishing what you've lost. Here's how it should all break down.
Sip Slowly Throughout the Day
Hydrating for a workout shouldn't mean chugging 20 ounces of water immediately beforehand. Aside from the obvious (a sloshy stomach that's not conducive to exercise), there's another reason why drinking small amounts all day long is better than trying to get it in all at once: Your body can hang onto it longer.
Why, you ask? It turns out, drinking a lot of liquid in a short amount of time causes a drop in antidiuretic hormone, or ADH, a chemical naturally produced by the body to help conserve fluids. "When that hormone drops, the body wants to urinate," says Stavros Kavouras, a hydration scientist at the University of Arkansas. "This is a phenomenon that takes place even if you are not well hydrated."
So even if you've been skimping on water for the past few days, he explains, your body won't have much use for that pint you chug pre-run. (Plus, you'll probably have to pee en route.) Sipping throughout the day, on the other hand, keeps ADH levels steady.
Make Hydration a Habit
Of course, we don't always drink as much water during the day as we should. Always having a glass or bottle of water within reach can help you make it a habit, Kavouras recommends. Drinking from a straw may help you drink more without realizing it, too.
The temperature of the water makes little difference in how it's used in your body, Kavouras says, but most people find cool water more palatable and may be more likely to drink it that way. The same goes for sparkling water, mineral water, or water that's marketed as alkaline or oxygenated: "If you enjoy the taste, go for it." says Kavouras, "but there's no evidence that it works any differently in the body."
Foods with high water contents (like fruits and vegetables), also contribute to your overall hydration. Instead of aiming for a certain number of ounces a day, use your bathroom trips as a guide. "If you go when you get to work in the morning and you don't have to go again until you leave in the evening, you're not drinking enough," says Kavouras. (Your urine should be an indicator, too: Aim for a light yellow, pale straw color.)
During Your Workout: Drink When Thirsty
Use the same gradual approach to drinking fluids while you exercise, as well: Sip water or sports drinks regularly, but don't overdo it. New guidelines published in the Clinical Journal of Sports Medicine advise athletes to drink only when thirsty, because of the dangers of exercise-associated hyponatremia—a condition in which the body loses too much sodium due to excessive water consumption. "The normal range for sodium is very tight," says Tamara Hew-Butler, who co-authored the paper. "Dehydration makes cells shrink like raisins, while hyponatremia makes cells swell like over-watered grapes." But dehydration and water-weight loss during exercise do not impair performance until they approach 5 to 7 percent—not just 2 or 3 percent, as once believed.
Once the hard work is done (and your ADH levels return to normal), now's the time to refill your stores with a big glass of ice water. How much you drink should depend on how much you've sweat; Kavouras recommends this rule of thumb from the American College of Sports Medicine: Weigh yourself before and after, and drink 20 to 24 ounces for every pound lost.