It’s a little known problem, really. Many athletes are unaware it’s even possible. You can die from drinking too much water?

What?

But before you put down your Evian, understand that water intoxication, or hyponatremia, is pretty rare.

According to the American Medical Athletic Assn., hyponatremia is caused by low levels of sodium in the blood.

Ann Chapman, a registered dietitian and coordinator of nutrition services at Kansas University’s Watkins Memorial Health Center, says athletes who overhydrate face serious – sometimes fatal – consequences.

“It is an increasing problem with runners and marathoners. They are not using a glucose replacement solution, so what happens is they are getting really sick during races and being misdiagnosed as dehydrated,” she says.

That’s because dehydration shares many symptoms with its dangerous counterpart: dizziness, nausea, cramps and headaches. When an overhydrated person is diagnosed as dehydrated, the first thing they are told to do is drink water. That “treatment” can be enough to cause life-threatening seizures, sometimes resulting in a coma. To stop misdiagnoses, most endurance event staff members prick an athlete’s finger to check for sodium levels.

Richard Demby, then a sophomore at Lawrence High School, takes a drink of water during a break at the 2005 Kansas Relays in April at Memorial Stadium. Runners, especially those who specialize in long distances, are at minor risk for hyponatremia, or water intoxication.

At KU, Dr. Lawrence Magee, head team physician for the KU Athletic Corp., says hyponatremia isn’t a problem his trainers have to worry about too much.

“The longest races our athletes are involved in are about 10,000 meters,” he says. “It’s more of a marathon runner’s problem, so I can’t remember one of our athletes being affected by it. I guess that’s good for us because it’s a very serious thing to deal with.”

Magee is right. Endurance athletes – those competing in activities for more than four hours – are the ones who should take special precaution against water intoxication.

Others at risk are athletes on low-sodium diets, beginning marathoners who run slowly and pay careful attention to hydration, and salty sweaters (athletes whose body and clothing are covered in white residue after a workout). Women seem to be more prone to hyponatremia than men, but there is no biological reason behind the difference. According to the Gatorade Sports Science Institute, it seems women are simply more vigilant about their hydration.

The biggest secret to keeping hydration in check is found in the scale.

Weigh yourself before you work out and again when you are finished. If you gained weight, you drank too much; if you lost weight, you drank to little. Endurance athletes can help replace lost sodium by eating salty snacks, such as pretzels, during their race and choosing sports drinks, such as Gatorade, instead of water.