Staying hydrated is critical for feeling good and operating at your best. Given that the body is made up of an average of 60 percent water (though this amount varies from person to person), it requires H20 to function on numerous levels. You need more than two hands to count the number of awesome things water does within your body, but some of its main jobs include removing waste and toxins, regulating body temperature, lubricating joints, and improving cellular, tissue, and organ health, says Tamika Henry, MD, MBA, board-certified family physician and founder of Unlimited Health Institute in Pasadena, Calif. Other tasks include aiding in saliva production, proper digestion, and the delivery of oxygen throughout your body.
Throughout the day, we naturally use and lose water—we sweat, we pee, we exhale—and can't actually produce more of it by ourselves. Therefore, we rely on external sources to replenish properly. When you lose more water than you take in, you're considered dehydrated. But you probably don't track whether you're dehydrated by keeping tabs on your water intake and output—you more likely wait until you feel thirsty. But here's the kicker: "If you're thirsty, you're already mildly dehydrated," Dr. Henry says.
While thirst is the most common signal of dehydration—and you should absolutely listen to it—there are several other, less-obvious ways to tell if you're water-deprived, including some mental and emotional markers that may surprise you.
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Mental and Physical Signs of Dehydration
You have bad breath.
Bad breath has many causes, including dehydration. Why? Because saliva has antibacterial properties, and the creation of saliva requires water. When you're dehydrated, salivary production goes down because your body has to do some hydration triage and divert fluids to its higher-priority locations. "The ability to fight odor-causing germs in your mouth may not be efficient [when you're dehydrated], causing bad breath," explains Shyamala Vishnumohan, PhD, director of food and nutrition and certified prenatal dietitian at One to One Consulting in Perth, Australia.
You feel hungry.
First things first: It's very possible that you're actually hungry, in which case, please eat! But there are times when you feel peckish or notice cravings (often for salty foods) because you're really thirsty, Dr. Henry says. It's important to pay close attention to your body and learn the difference—not because you shouldn't be eating, but because your body is trying to tell you that it needs water. Next time you feel hungry, but aren't sure why—maybe you just ate or don't usually feel hungry around that time—ask yourself, "am I dehydrated?" Drink a glass of water and wait about 15 minutes. "More times than not, people are thirsty and not experiencing an actual need to eat," she says. And heads up, you might be thirsty and hungry, so grab yourself a glass of water and a satisfying snack.
Your head is pounding.
There's no certain explanation for why headaches occur with dehydration, but experts have a few hunches. "A working theory involves pain receptors in the brain that are attached to the meninges (membrane layers that protect your brain and spinal cord)," Dr. Henry says. Being dehydrated can cause fluid to shift out of the brain, putting pressure on the meninges and stimulating pain receptors as a result. Translation: that headache is a possible clue that you've gone too long without water.
Your focus is off.
If you're having trouble focusing, it might be wise to slug some water. "Dehydration can lead to a lack of ability to focus, causing short-term challenges in performing tasks related to motor and visual skills," Dr. Henry says. Even mild dehydration can cause cognitive issues, which is why she recommends setting alarms throughout the day to remind you to drink.
Constipation is the worst. It's defined as having less than three bowel movements per week, and it's common among Americans—roughly 16 out of 100 adults have symptoms of constipation, according to the National Institute of Diabetes and Digestive and Kidney Diseases. One of the culprits of constipation may be dehydration. Water aids digestion, Dr. Henry says, and in the end, is one of the most helpful keys to keeping things moving and regular.
While lack of sleep is largely responsible for a negative mood—and we all know feeling "hangry" is definitely a thing—dehydration can also play a role in spoiling your state of mind. Feeling cranky, impatient, or annoyed? "Dehydration can cause neurological effects that lead to irritability," Dr. Henry says. So next time you snap at your partner or the kids, it may have less to do with their behavior and more to do with your need for water.
Your skin feels less elastic.
While dry skin is not necessarily a direct sign of your hydration levels, skin elasticity is. Have you ever pinched your hand to see if it snaps quickly back into place? If it doesn't, it turns out this is a pretty effective way to tell if you're dehydrated, Vishnumohan says. To test, use two fingers to pinch your skin on the top of your hand, lower arm, or abdomen. If you're hydrated, it should tent up and release, snapping back into place immediately. When you're dehydrated, on the other hand, your skin loses some of that elasticity it needs to snap back immediately.
How Much Water Should You Drink?
The short answer: It depends.
The long answer? Research has found that, "there is no single daily water requirement for a given person." It's not easy to say exactly how much you need because it truly depends on a range of factors, including body size and composition, physical activity levels, climate, and diet. If you're spending time in hot weather or performing strenuous exercise, for example, you'll need to replace fluids lost from sweating by drinking even more (and don't forget to replace lost electrolytes, too).
Some experts suggest drinking roughly half your body weight in ounces (i.e. if you weigh 160 pounds, you should consume about 80 ounces of water). And you've probably heard the guideline to drink about eight 8-ounce glasses of water a day. But there's no scientific evidence to conclude that these recommendations are the standard, be-all and end-all rule for every individual, Vishnumohan says.
Instead of agonizing over ounces or glasses, aim to drink water regularly throughout the day and listen carefully to your body's natural cues. Remember that many foods (fresh fruits and veggies!) and beverages besides water (tea, milk, smoothies!) also contribute to your hydration status. Vishnumohan's hydration habits, for instance, include enjoying a cup of coffee in the morning and a cup of tea at night, eating five servings of vegetables and two servings of fruit each day, and drinking at least one glass of water with every meal.