With extremely hot temperatures in many parts of the country, staying hydrated is even more important than ever. But a 36-year-old daycare worker from Monticello, Indiana, who had two young daughters, died unexpectedly last month after drinking too much water on a boating trip. Ashley Summers downed four bottles of water in 20 minutes and passed out at home later that day and never regained consciousness.

Summers’ brother Devon Miller, told WLFI news that his sister died of water intoxication.

“It’s relatively rare,” said emergency physician Dr. Alok Harwani, adjunct clinical assistant professor of emergency medicine at Indiana University School of Medicine. “What we are concerned about is just drinking too much water in a short period of time. Your kidneys can only clear about a liter of water per hour.”

According to Insider, water intoxication, also known as water toxicity, happens when drinking too much water, too fast, throws off the body’s electrolyte balance causing the sodium levels to drop rapidly. Sodium helps maintain blood pressure and is vital for the healthy functioning of nerves, muscles, and body tissues. When the amount of sodium outside the cells drops below normal because of excess water consumption, water moves into the cells to balance the levels and the cells begin to swell. When brain cells swell it could be deadly.

When Summers drank all that water, her sodium levels became too low, causing her cells to fill with water and swell, including the cells in her brain. “It pinched off her blood vessels like a kink in a hose and just stopped the blood flow to the brain,” said Miller.

Harwani cautioned that to prevent seizures, coma, or death from water intoxication, split up water intake with drinks like Gatorade, Pedialyte or snacks like fruit, vegetables, or granola bars to replenish electrolytes.

Frances Largeman-Roth, a registered dietitian, told Today that drinking a glass of water with some salt added can be beneficial if you’ve been working out in extreme heart and lost a lot of sweat.

“Adding a little fruit juice, such as orange or watermelon, to the salty mix would also be smart because carbohydrates stimulate the absorption of sodium and water, both during and after exercise,” she says.

Be aware of the symptoms of water toxicity.

“Things to look for are if you are really feeling out of it, very tired, very fatigued,” said Harwani. “Sometimes patients feel like they’re starting to have a mild headache, or just feeling overall unwell. Those could be signs of water intoxication.”

Usually, people who perform long workouts and lose both water and electrolytes from their bodies are at most risk for water toxicity.

“If you are concerned that you or a family member is not acting right and you are worried about water toxicity, don’t hesitate to call 911,” says Harwani. Once identified, water intoxication requires hospital treatment.