Can You Drink Too Much Water?

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You've heard it a million times. When it's hot outside or you're exercising, drink lots of water. It's how your body stays hydrated.

But can there be too much of a good thing? In rare cases, drinking an extreme amount in a short time can be dangerous. It can cause the level of salt, or sodium, in your blood to drop too low. That's a condition called hyponatremia.It's very serious, and can be fatal. You may hear it called water intoxication.

How much would you have to drink? An enormous amount. Gallons and gallons of water.

"These are very isolated cases, and this is extremely rare," says Sharon Bergquist, MD. She's an assistant professor of medicine at Emory University School of Medicine in Atlanta. "More people by far and away are dehydrated, [rather] than having a problem with over-hydration."

What Is Water Intoxication?

If you drink a bottle of water here and there when you exercise or when you're hot, you’ll be fine. Where you run into problems is drinking way too much too fast.

"Young, healthy people don’t normally [get hyponatremia] unless they drink liters and liters of water at once, because your kidneys can only [expel] about half a liter at most an hour," says Chris McStay, MD. He's an emergency medicine doctor at the University of Colorado School of Medicine. "You're drinking more than your kidneys can pee out."


The issue boils down to sodium levels. One of sodium’s jobs is to balance the fluids in and around your cells. Drinking too much water causes an imbalance, and the liquid moves from your blood to inside your cells, making them swell. Swelling inside the brain is serious and requires immediate treatment.

Sometimes babies can have issues. Their bodies are so tiny that they can't handle lots of water. That's why doctors say infants should drink only milk or formula.

Then there are the cases like hazing rituals and publicized contests where people drink large amounts on purpose.

Symptoms and Treatment

The warning signs of hyponatremia look a lot like the symptoms of heatstroke and exhaustion. You might be hot, have a headache, and just feel crummy. Other early symptoms can include diarrhea, nausea, and vomiting.


"If you see someone like that, pull them aside, put them in the shade, and talk to them," McStay says. It’s often hard to tell the difference, he says, between water intoxication and heat exhaustion, “unless you know they drank 6 gallons of water."

If you don't get help right away, the condition can quickly lead to swelling in the brain, seizures, and coma. Get to an emergency room as soon as you can. Doctors there can inject concentrated salt water to ease swelling and reverse problems.

Advice and Prevention

The best way to prevent hyponatremia is to make sure you don't drink way more than you sweat out. But that's hard to measure.

Experts say drink until you don't feel thirsty, then stop. Or check things out when you go to the bathroom.

"I tell people to look at your pee," McStay says. "If it's dark, you're probably dehydrated, and you should drink. But you wouldn’t want to be peeing, peeing, peeing, and it's clear. Then you're peeing out almost clear water and you have a problem."

Sometimes, it helps to have sports drinks instead of plain water if you know you'll be working hard. Sports drinks have sodium and other electrolytes. But too much liquid of any kind too fast can cause issues.

We’ve always been told to stay hydrated while exercising, Bergquist says. “But there's a fine line. It's important to listen to your body. If you're pushing fluids beyond the point it's comfortable, it's a sign it's time to stop drinking."

WebMD Feature Reviewed by Michael W. Smith, MD on August 14, 2014



Sharon Bergquist, MD, assistant professor of medicine at Emory University School of Medicine.

Children's Hospital St. Louis: "Water Intoxication in Infants."

Chris McStay, MD, FACEP, FAWM, Chief of Clinical Operations, Department of Emergency Medicine, University of Colorado School of Medicine.

Noakes, T. Nutrition Issues in Gastroenterology, September 2008.

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