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What’s It Mean?

It’s when you lose more water than you take in. That makes it harder for your body to do some basic jobs, like keep your temperature steady and clear out waste. You lose water in your sweat, tears, and every time you go to the bathroom. Even breathing takes a little out of you. 

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woman with headache
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How Lack of Water Affects You

More than half your body weight comes from water. So if your levels are off, it can show up in a surprising number of ways. Mild dehydration can make you feel tired, give you a headache, and affect your mood and focus. And when you push yourself hard at the gym, all that sweating actually lowers how much blood you have for a bit.

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glass of cold water
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Is Thirst a Sign I’m Dehydrated?

Yes, but no need to panic. By the time you get the urge to quench your thirst, you’re already a little dehydrated. As long as you pay attention and snag a drink when your body tells you to, it’s not a problem. For older adults, the lag might be a little longer. So it can help to make a habit of drinking water.

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sick child in bathroom
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Who’s It Likely to Happen To?

You can lose over a gallon of water a day if you have diarrhea and throw up. Babies and kids are more likely than adults to get dehydrated because they're smaller. Older adults need to be on the lookout because your sense of thirst gets duller with age. Kidney disease and some health conditions can make your body get parched. Pregnant or breastfeeding women need to drink more than usual.

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Symptoms in Young Children

Babies and little kids can’t always tell you what’s going on with their bodies. Look for a dry tongue, no tears when crying, no wet diapers for 3 hours, and more fussiness than normal. When it’s more severe, their mouths will be dry and sticky, and their eyes and cheeks may look sunken. They also may breathe fast and have a fast or weak pulse. 

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crack in dry earth
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Symptoms in Older Kids and Adults

You might be thirsty, and your mouth might feel dry or sticky. You won’t pee very often -- under 4 times a day. When you do go, there may not be much pee, and it’ll be dark or have a strong smell. You may feel dizzy or lightheaded, and you may pass out. As it gets worse, your thirst cranks up. Your breathing and heart rate may be faster than normal. You can overheat, and you might feel confused or cranky.

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bottled water
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Should I Drink 8 Cups a Day?

This old rule has zero science behind it. But it’s fine as a rough guide. The amount you need to drink depends on how active you are, where you live, and your overall health. If you’re not sure you’re drinking enough, check the color of your pee. Clear or pale yellow means you’re all set. Darker means you need to drink up. 

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What About Electrolytes?

They’re just basic salts, like potassium, sodium, and calcium. But they have a hand in everything from how your nerves work to building healthy bone. Your electrolyte levels are closely tied to how much water is in your body. That means that if you’ve lost a lot of fluid, you’ll feel thirstier and pee less as your body tries to get the electrolytes back in balance.

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Do I Need a Sports Drink?

Almost never. These blends of water, salts, and sugars are made for high-level athletes, like marathon runners. Most of us don’t need anything more than water during exercise. You’ll only have to work harder to burn off the extra calories from sport drinks. If you do intense training for more than an hour, then they can make sense. 

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Oral Rehydration Solution

When dehydration is mild or even moderate, you can often kick it with plenty of water. But if you have severe diarrhea or are throwing up, an oral rehydration solution might help. It’s more often kids who need one. The special mix of salts and sugars is a closer match to what the body needs. You can buy it over the counter at a drugstore.

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When to Call Your Doctor

When you see symptoms of severe dehydration, call your doctor right away. It can hit kids quickly, so it’s best to check in sooner rather than later. Signs include:

  • Diarrhea for more than 24 hours
  • Feeling dizzy, confused, or faint
  • Can’t keep fluids down
  • No energy
  • Fast heartbeat or breathing
  • Black or bloody poop
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Emergency Treatment

When your water levels get too low, you can’t tackle dehydration on your own. You’ll need to be treated at a hospital. The idea is the same -- to get fluids in you and to get your body back in balance. Doctors will give you the treatment through a vein with an IV, because it gets water and salts into your body much faster than you’d be able to drink them.

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Can I Drink Too Much?

You can, but it’s not very likely. When you drink more than your kidneys can handle -- and that’s a lot -- you end up with a condition called hyponatremia. This is when your sodium levels get very low, causing your cells to swell up. It can be deadly, but rare. It mostly only happens to people who compete in intense long-distance races. 

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Tips for Staying Hydrated

If you just can’t remember to drink enough water, look for ways to build it into your day. Make water your go-to drink. Tip a glass at and between each meal. Or set a reminder on your phone to have a glass every hour. Some people find that carrying a water bottle does the trick. And if you’re hankering for a snack, have water instead. Sometimes, our bodies confuse thirst for hunger.

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Sources | Medically Reviewed on 02/19/2020 Reviewed by Jennifer Robinson, MD on February 19, 2020


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Mayo Clinic: “Dehydration,” “Water: How much should you drink every day?” “Hyponatremia.”

KidsHealth: “Dehydration,” “First Aid: Dehydration.”

FamilyDoctor.org: “Hydration: Why It’s So Important.”

University of Connecticut, UConn Today: “Even Mild Dehydration Can Alter Mood.”

U.S. National Library of Medicine: “Water, Hydration and Health.”

Merck Manual: “About Body Water.”

American College of Emergency Physicians, Emergency Care for You: “Dehydration Comes on Fast and Can Be Fatal.”

National Health Service (UK): “Dehydration.”

HealthDirect: “Dehydration.”

Pubmed: “ 'Drink at least eight glasses of water a day.' Really? Is there scientific evidence for '8 x 8'?”

University of New Mexico, Comprehensive Cancer Center: “Electrolyte Imbalance.”

Health Navigator New Zealand: “Oral Rehydration Salts.”

Harvard Health Publishing, Harvard Medical School: Trade sports drinks for water.”

University of Wisconsin Health: “Sports and Energy Drinks: Are They Necessary?”

Reviewed by Jennifer Robinson, MD on February 19, 2020

This tool does not provide medical advice. See additional information.

THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for general informational purposes only and does not address individual circumstances. It is not a substitute for professional medical advice, diagnosis or treatment and should not be relied on to make decisions about your health. Never ignore professional medical advice in seeking treatment because of something you have read on the WebMD Site. If you think you may have a medical emergency, immediately call your doctor or dial 911.