The Surprising Dangers of Drinking Too Much Water

How common is overhydration?

That’s the good news: It’s extremely uncommon. 

“The possibility of developing a seizure or a major side effect of drinking too much is extremely rare,” Kavouras says. “Your body can respond to it.”

To become overhydrated to the point of developing hyponatremia, you would have to not only drink double the recommended amount of fluids, but you would need to do so quickly, Kavouras says.

“It doesn’t happen easily,” he says.

Case in point: Overhydration is often seen in endurance athletes, like marathoners, because they tend to consume large quantities of water during extended physical activities without adequately replacing lost electrolytes like sodium through sweat.

“They’re drinking above and beyond what they’re sweating out, putting them at high risk of developing hyponatremia,” Kavouras says.

A study looking at Boston Marathon runners, published in The New England Journal of Medicine, found that a substantial number of runners had abnormally low serum sodium concentrations at the end of the race.

The culprit? Overhydrating.   

It’s easy to forget that sodium is an essential nutrient that helps to maintain the balance of fluids inside and outside of cells. When sodium levels drop due to excessive water consumption, fluids travel from the outside to the inside of cells, causing them to swell.

“Sodium has gotten a bad name because most people consume way more sodium than is necessary,” Kavouras says. On average, Americans eat more than 3,400 milligrams of sodium each day, the American Heart Association says, which is more than double the recommended 1,500 mg per day.

“It’s a very common perception that low-sodium is a healthy diet, but if you are physically active and you lose more sodium via sweating — and in combination with that drink a massive amount of plain water — then that combination could create a mild sodium deficiency,” Kavouras says.

Surprisingly, older adults are also at risk of overhydration for a number of reasons, including:

• Reduced kidney function, making it more challenging for the body to efficiently regulate fluid balance.
• Certain medications that can affect fluid and electrolyte balance, such as diuretics.
• Preexisting medical conditions such as heart failure, which can lead to fluid retention and an increased risk of overhydration.
• A decreased thirst perception, which can result, curiously, in dehydration or overhydration if you consume fluids without being adequately thirsty. What’s more, the sensation of thirst tends to decline with age.

Far more common than drinking too much? Drinking too little — especially among older adults.

“If you look at the national data, more than 85 percent of older adults don’t drink an adequate amount of fluid,” Kavouras says.

There are a few clues that can let you know if you’re well-hydrated, such as if you’re going to the bathroom roughly every two to three hours and your urine is light colored, suggests a study published in 2021 in the European Journal of Clinical Nutrition.

“These are the best predictors that you’re well-hydrated,” says Kavouras, who was lead author on the study. “If you’re going more often, then you’re overdoing it. That should guide your fluid intake. If you drink all day and pee every hour, then this is an indication that you’re drinking way too much.”