Water is considered one of the least toxic chemical compounds, with an LD50 exceeding 90,000 mg/kg (90 g/kg) body weight in rats;[3] drinking six liters in three hours has caused the death of a human.

[6] A study conducted on runners completing the 2002 Boston Marathon found that thirteen percent finished the race with hyponatremia.

Persons working in extreme heat and/or humidity for long periods must take care to drink and eat in ways that help to maintain electrolyte balance.

This condition can be especially dangerous if the patient also exhibits other psychiatric indications (as is often the case), as the caretakers might misinterpret the hyponatremic symptoms.

The swelling increases intracranial pressure in the brain, which leads to the first observable symptoms of water intoxication: headache, personality changes, changes in behavior, confusion, irritability, and drowsiness.

These are sometimes followed by difficulty breathing during exertion, muscle weakness and pain, twitching, or cramping, nausea, vomiting, thirst, and a dulled ability to perceive and interpret sensory information.

As the condition persists, papillary and vital signs may result including bradycardia and widened pulse pressure.

Both cerebral edema and interference with the central nervous system are dangerous and could result in seizures, brain damage, coma, or death.