A glass of good old water can cure everything from headaches to fatigue. Gulp down the latest information on getting your fill, deliciously.

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Getty Images Whatever the latest food trend—chia seeds, coconut flour, kale chips—you're on it. But you might be skimping on the most basic thing you can do for your health: chugging enough water.

"I see this happening a lot with busy women," notes Pamela Peeke, MD, professor of medicine at the University of Maryland and author of Body for Life for Women. "They become so absorbed with work, answering e-mails and texting that they neglect to grab a water bottle." Soon they're parched and draggy.

Other signs of mild dehydration: muscle cramps, dizziness and headaches. Women who are even slightly dehydrated may find it harder to concentrate than those who aren't, according to a recent study in The Journal of Nutrition. And if your body is regularly running low on water, you're more likely to be constipated, too.

Dehydration tends to happen most during the summer months. "On top of transporting nutrients to your cells and protecting your kidneys, water regulates body temperature," Dr. Peeke explains. As you heat up, your skin starts pumping out water to cool you off, which can put you at a deficit if you're not careful. But don't sweat it—our expert guide makes it easy to stay quenched all season long.

How much fluid should I drink every day?
You've probably heard you should have eight glasses daily, but it turns out that's a little low. (This popular recommendation has been around mainly because it's easy to remember—8 ounces eight times per day.) "A good baseline is 2.2 liters, or about 9 cups of fluid a day," Dr. Peeke says. You may need even more if you're overweight, live at a high altitude or are working in extremely hot weather, all of which are dehydrating factors. Experts agree that your best gauge is that time-tested one: checking your pee. "You want it to be the color of lemonade," says Kim Larson, RDN, spokesperson for the Academy of Nutrition and Dietetics. If it's medium to dark yellow, down a glass, stat. Sorry, but you don't get any bonus points for clear urine, a sign that you're actually drinking more than you need. According to a major review published in the Journal of the American Society of Nephrology, there's no significant evidence that guzzling extra glasses will help flush your body of toxins, improve skin tone or reduce headaches any better than being adequately hydrated will.

But wait—don't I have to get more when I exercise?
That depends. If you'll be indoors and have managed to stay hydrated all day before the workout, then no. But if you're in the summer heat, you can easily sweat out the equivalent of 4 cups of fluid in an hour-long outdoor session. In that case, drink 20 ounces of water an hour before, and try to take in about one half of a cup during every 15 minutes of activity, Larson advises. Going for a jog first thing in the morning? Have a drink beforehand. And if you're training for a marathon or playing a sport for a few hours, weigh yourself before and after, says Leslie Bonci, RD, a sports nutritionist at the University of Pittsburgh Medical Center: "For every pound you've lost during your workout, drink 24 ounces of fluid to get hydrated again."

Does my daily morning coffee count?
Surprise: It does, per a new study from the University of Birmingham in England. Researchers asked java drinkers to sip either coffee or water and found that caffeine isn't dehydrating. There's a caveat, though. If you never drink caffeine and then have a cup of coffee, it acts as a diuretic and draws water from your body, explains Leslie Spry, MD, spokesperson for the National Kidney Foundation. "But if you have coffee regularly," he adds, "your body becomes habituated and it doesn't have the same effect." Other beverages, including tea, milk, OJ and sports drinks, also work, although you don't want to overcaffeinate or down too much sugar. What to avoid? Soft drinks, even diet kinds. "They have salt, which dehydrates you," Dr. Peeke says. "So many women think, Ahh, how refreshing! But soda just sucks fluid out of your cells."

How much does the water that I consume from foods like fruit matter?
Water in food accounts for about 20 percent of people's daily fluid needs, according to the Institute of Medicine. "And the hydration you get from food is just as good as what you get from drinking water," says Dr. Peeke. For example, a grilled chicken breast, served with cauliflower and one-half cup of spinach, nets you almost a full cup of water. There's even a hidden perk to watery bites: They may help you slim down. (Here are 7 Foods That Help You Lose Pounds.)

If I drink a lot one day, does it make a difference if I don't have as much the next?
Reality check: You are not a camel. Human bodies weren't designed to store excess water. "After a couple of hours, you just pee it out," says Bonci. The reality is, you need to reach your H2O goal every single day to sidestep energy dips and other health troubles. If you tend to skimp, especially at times when you've got a lot going on, tap an app to help; try Waterlogged, which will send you reminders to drink up. The good news is that even if you get seriously thirsty and realize that you haven't been drinking enough water, your body will rebound after you down a glass or two. Cheers!

Do I need a water filter?
Despite mandated monitoring, "there can still be trace amounts of impurities in tap water, including lead that leaches from plumbing," explains Cheryl Luptowski, home-safety expert for NSF International. Even very low levels of lead in water have been linked to cognitive issues, particularly in children. First, call your supplier to get your water report. A simple carbon filter may be enough. But if there's just a tiny bit of arsenic, lead or perchlorates, you'll need a home filtration system designed for your issues. Compare models at nsf.org. Cost: $150 to $1,000.

Four sneaky things that parch your skin—and how to keep your complexion radiant:

The superhigh office AC
"Cool air lacks humidity—which means it takes water from elsewhere, including your skin," says Debra Jaliman, MD, author of Skin Rules. Apply a refreshing gel moisturizer with hyaluronic acid, which locks in water better than your average moisturizer. Try SkinCeuticals Hydrating B5 gel ($78; Amazon.com).

Fun in the sun
Exposure can deplete your skin's natural oils, even if you wear sunscreen. And pool chlorine can be extremely drying, so shower off ASAP and rub in lotion while skin is still damp. At night, apply a facial moisturizer with glycolic acid, such as Olay Regenerist Night Resurfacing Elixir ($30; Amazon.com).

Happy hour
Alcohol is dehydrating, and summer faves like margaritas and Bloody Marys are also salty. Head off problems by having a glass of water between drinks—with a cute little cocktail umbrella, if it helps.

Your bedtime routine
You may be tempted to use an alcohol-based toner in the summertime to clear up excess oil, but it can leave your skin too dry. Better to go with an oil-removing cleanser. Try Biore Deep Pore Charcoal cleanser ($8; Walgreens.com).