Drinking water excessively can have a number of side effects, including muscle cramping from electrolyte imbalance and an increase in urine frequency. In extreme cases, drinking too much water can lead to fatal water intoxication, also known as water toxemia, water poisoning, or hyperhydration.
“In overhydration an excess of water dilutes the electrolyte concentrations in the blood, causing imbalance throughout the body’s many systems,” physician Catherine Waldrop, M.D., tells mbg. Electrolytes, like sodium, potassium, magnesium, and calcium, are charged ions essential for many cellular processes. “When the concentration of electrolytes in the blood is too low, it makes nearly all cellular processes less efficient to nearly impossible,” she says.
The most common electrolyte imbalance, which can be caused by drinking too much water, is called hyponatremia (aka low sodium in the blood). “Mild hyponatremia is characterized by gastrointestinal tract symptoms, nausea, vomiting, loss of appetite,” one study says, whereas, more serious cases result in excess water and swelling in the brain, leading to seizures, comas, or impaired mental status.
This seemingly crazy phenomenon is more common for people going through intense training programs, including triathlon or ultramarathon runners, members of the military, or professional athletes. According to the U.S. National Library of Medicine, extreme thirst could also be triggered by medications like diuretics, or a symptom of high blood sugar.