During the steamy summer months, lots of attention is focused on dehydration and making sure we prevent it by drinking enough water. But, though less common, overhydrating can also lead to health problems.

Roberta Anding, RDN, a sports dietitian at Rice University in Houston, puts it like this: “If I pull the wheel too hard to the left and end up in a ditch, I’m dehydrated. If I pull too hard to the right, I’m overhydrated. Neither one of those is conducive to performance.”

One consequence of drinking too much water, which is sometimes called water intoxication, is hyponatremia. This condition occurs when the blood’s sodium level drops below 135 milliequivalents (mEg) per liter (L), per the Mayo Clinic. (The Mayo Clinic notes that normal blood sodium level is 135 to 145 mEq/L.)

Excessive water consumption dilutes electrolytes in the blood, such as sodium, says Mitchell Rosner, MD, a nephrologist with the department of medicine at the University of Virginia in Charlottesville. When the sodium level drops too quickly, fluids move out of the bloodstream and into tissue cells, which causes these cells to expand. In extreme cases, Dr. Rosner says, your brain can’t accommodate such intense swelling, resulting in neurological issues or even death.

What Causes Hyponatremia?

Hyponatremia is the most common electrolyte disorder, according to research published in August 2016 in the American Journal of Medicine. It’s particularly prevalent among endurance athletes who drink large volumes of water before, during, and after exercise: One previous study suggested that 13 percent of participants in the 2002 Boston Marathon experienced hyponatremia.

The condition has also occurred during contests in which people set out to drink extremely large amounts of fluids. (In 2007, for example, a 28-year-old woman died of water intoxication following a California radio station’s water-drinking contest.)

Hyponatremia also commonly affects people with severe mental illness, like schizophrenia, who feel compelled to drink a lot of water, says Chris McStay, MD, an associate professor with the department of emergency medicine at the University of Colorado in Aurora.

“The most common thing is that, in the summer when people are told to drink a lot, they maybe take it a little bit too far,” Dr. McStay says. “If you’re drinking 2, 3, or 4 liters an hour, and you’re not losing a ton by sweating, you basically begin to exceed the amount that the body can excrete. And that’s when you get in trouble.”

According to the Mayo Clinic, other potential causes of hyponatremia (which can occur in different severities, ranging from mild to severe, and have different onset periods, from slow to rapid) include:

Medications that can interfere with hormone and kidney function, such as diuretics or antidepressants
Certain heart, liver, and kidney conditions
Chronic diarrhea or vomiting
Hormonal changes, such as adrenal gland insufficiency or low levels of thyroid hormone
Taking the drug ecstasy

How Much Water Should You Drink?

The U.S. National Academies of Sciences, Engineering, and Medicine recommend drinking 15.5 cups (3.7 liters) of fluids a day if you are a man and 11.5 daily cups (2.7 liters) if you are a woman.

The exact amount of water you need each day depends on factors like your age, sex, activity level, and how hot it is outside. But one easy way to know how much you need to drink is to trust your own body, Rosner says.

“Thirst is an evolutionarily conserved mechanism to make sure that we drink an adequate amount of fluids but not too much,” he explains. “What I tell people is to get a sense of your thirst. Drink until you’re not thirsty, but don’t drink above that. And if you do that, you’ll be fine.”

Signs You're Drinking Too Much Water

Many of the symptoms of hyponatremia overlap with those for heatstroke, heat exhaustion, and dehydration, McStay says.

According to McStay and Anding, symptoms of hyponatremia include:

Nausea or vomiting
Headache
Bloating
Swollen hands and feet
Muscle spasms or cramping
Tiredness
Altered mental state
Restlessness and irritability

Daily weigh-ins can help you figure out if you’re drinking too much water, Anding says. If you’re worried about getting dehydrated — say, if you have plans to work outside, and you know you’ll be drinking a lot of water — weigh yourself at the start of the day. If you’ve gained 10 or more pounds by the end of the day, she says, it’s a good time to ask yourself: Could this be hyponatremia? (But again, hyponatremia isn’t a common phenomenon, so these weigh-ins make the most sense for people in extreme circumstances, like running a marathon or participating in military training.)

Anding suggests writing down any symptoms you’re experiencing, such as nausea or a headache, and then calling your doctor. “What you're doing is collecting your own data,” she says. “Then you can tell your doctor, ‘I was out working in the yard, and I gained 10 pounds because I was drinking water all afternoon.’” Your doctor can likely help you figure out whether you need to go to the emergency room, she says.

Complications of Hyponatremia

Hyponatremia can lead to seizures, coma, and severe neurological symptoms, including brain damage. Dying from drinking too much water is rare, but as noted, it has happened.

“When sodium [levels] gets really low — I’m talking 100 mEq/L or a number that’s dramatically different than the normal range — you can die, because your brain will swell up so much,” McStay says. “The brain stem pushes down the skull base, which makes you stop breathing and lose consciousness.”

Outlook of Hyponatremia

Your doctor can diagnose hyponatremia based on blood tests and urine tests. The symptoms of this condition are usually mild, and patients can recover at home.

But in severe cases, patients need to be treated in the hospital, McStay says: “At some point, things start to happen that your body can’t fix quickly enough. The ability for the kidneys to excrete your water isn't good enough or fast enough to correct the situation.”

If you’re experiencing symptoms like an altered mental state or seizures, it’s important to seek urgent medical attention, rather than simply making a doctor’s appointment.

If you have severe hyponatremia, correcting it too quickly can be dangerous. In this case, your doctor will likely give you a sodium solution via an IV to slowly raise the sodium level in your blood. You may also be given medication to help cope with the side effects of hyponatremia, such as headaches and nausea.

“Unfortunately, we get case reports of people passing away from [hyponatremia], but that's really very rare,” Rosner says. “Most people either recover spontaneously or with medical treatment. They do very well.”

A Final Word on Hyponatremia

Hyponatremia, which occurs when the blood’s sodium level drops too low, can occur from drinking too much water. This isn’t a common condition, and some people who are more at risk include, for example: endurance athletes, those participating in contests that involve drinking a lot of fluid, those taking certain illicit drugs like ecstacy, and people with psychiatric conditions.

Pay attention to symptoms such as vomiting, bloating, and an altered mental state, and if you’re worried you might have consumed too much water, call your doctor, who can help you figure out if you need to seek emergency treatment. (When in doubt, seek emergency care evaluation, especially if your symptoms are severe.)

Drinking Too Much Water (Hyponatremia): What You Need to Know