Water intoxication

In normal circumstances, accidentally consuming too much water is exceptionally rare. Most deaths related to water intoxication in healthy individuals have resulted either from water-drinking contests, in which individuals attempt to consume large amounts of water, or from long bouts of exercise during which excessive amounts of fluid were consumed. In addition, water cure, a method of torture in which the victim is forced to consume excessive amounts of water, can cause water intoxication. Excess body water can also result from medical conditions or improper treatments, such as those causing hyponatremia.

Although 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, it can be considered a poison when over-consumed in a brief period; drinking six liters in three hours has caused the death of a human.

Risk factors

Low body mass (infants)

It can be very easy for children under one year old (especially those under nine months) to absorb too much water. This is due to their small body mass; it is relatively easy for infants to take in a large amount of water relative to body mass and total body sodium stores.

Endurance sports

Marathon runners are susceptible to water intoxication if they drink too much while running. This occurs when sodium levels drop below 135 mmol/L, which can happen when athletes consume large amounts of fluid. This has been noted to be the result of the encouragement of excessive fluid replacement by various guidelines. This has largely been identified in marathon runners as a dilutional hyponatremia. A study conducted on runners completing the 2002 Boston Marathon found that thirteen percent finished the race with hyponatremia. The study concluded that the strongest predictor of hyponatremia was weight gain while racing (over-hydration), and hyponatremia was just as likely to occur in runners who chose sports drinks as those who chose water.

Military training

Hyponatremia and other physical conditions associated with water intoxication are more often seen in those participating in military training. One US Army study found 17 trainees were admitted to a hospital over a year's period for water intoxication while another found that three soldiers had died, leading to a recommendation that no more than 1–1.5 L of water should be consumed per hour of heavy sweating.

Overexertion and heat stress

Any activity or situation that promotes heavy sweating can lead to water intoxication when water is consumed to replace lost fluids. People 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. People using drugs such as MDMA (often referred to colloquially as "Ecstasy") may overexert themselves, perspire heavily, feel increased thirst, and then drink large amounts of water to rehydrate, leading to electrolyte imbalance and water intoxication – this is compounded by MDMA use increasing the levels of antidiuretic hormone (ADH), decreasing the amount of water lost through urination. Even people who are resting quietly in extreme heat or humidity may run the risk of water intoxication if they drink large amounts of water over short periods for rehydration.

Psychiatric conditions

Psychogenic polydipsia is a psychiatric condition in which patients feel compelled to drink excessive quantities of water, thus putting them at risk of water intoxication. 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.

Iatrogenic

When an unconscious person is being fed intravenously (for example, total parenteral nutrition) or via a nasogastric tube, the fluids given must be carefully balanced in composition to match fluids and electrolytes lost. These fluids are typically hypertonic, and so water is often co-administered. If the electrolytes are not monitored (even in an ambulatory patient), either hypernatremia or hyponatremia may result.

Some neurological/psychiatric medications (oxcarbazepine, among others) have been found to cause hyponatremia in some patients.