The body needs water to function correctly, but drinking too much too fast can have serious health consequences. The kidneys can only remove 0.8 to 1.0 liters of water per hour, and a very high water intake can upset the body’s electrolyte balance.

It is difficult to drink too much water by accident, but it can happen, usually as a result of overhydrating during sporting events or intense training.

The symptoms of water intoxication can be vague, or unspecific— they can include confusion, disorientation, nausea, and vomiting.

In rare cases, water intoxication can cause swelling in the brain and become fatal.

This article describes the symptoms, causes, and effects of water intoxication. It also looks into how much water a person should drink each day.

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Also known as water poisoning, water intoxication is a disruption of brain function caused by drinking too much water.

Doing so increases the amount of water in the blood. This can dilute the electrolytes, especially sodium, in the blood.

If sodium levels fall below 135 millimoles per liter (mmol/l), doctors refer to the issue as hyponatremia.

Sodium helps 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.

When this happens to brain cells, it can be dangerous and even life threatening.

When a person consumes an excessive amount of water and cells in their brain start to swell, the pressure inside their skull increases. This causes the first symptoms of water intoxication, which include:

Severe cases of water intoxication can produce more serious symptoms, such as:

A buildup of fluid in the brain is called cerebral edema. This can affect the brain stem and cause central nervous system dysfunction.

In severe cases, water intoxication can cause seizures, brain damage, a coma, and even death.

Water intoxication is rare, and it is very difficult to consume too much water by accident. However, it can happen.

Water intoxication most commonly affects people participating in sporting events or endurance training or people who have various mental health conditions.

Sporting events

Water intoxication can occur in endurance athletes. It can happen if a person drinks a lot of water without correctly accounting for electrolyte losses.

For this reason, hyponatremia often occurs during major sporting events.

As the authors of one older study report, out of 488 participants in the 2002 Boston Marathon, 13% had hyponatremia symptoms, and 0.6% had critical hyponatremia, with sodium levels of less than 120 mmol/l.

The risk of hyponatremia is higher in sporting events involving long durations, high intensity work, and in those hot climates.

Military training

The Military Health System and Defense Health Agency reported 1,690 cases of exertion-related hyponatremia between 2007 and 2022 among active service members.

The symptoms of hyponatremia can be misinterpreted as those of dehydration, meaning that accurate diagnosis and appropriate treatment are essential.

For example, a 2015 report found that excess water consumption during a hot-weather 40-kilometer marching exercise caused a fatal outcome rather than prevented it. The soldier in question consumed almost 13 L of water during the exercise when peers drank closer to 10 L.

Mental health conditions

Compulsive water drinking, also called psychogenic polydipsia, can be a symptom of various mental health conditions.

It is most common among people with schizophrenia, but it can also arise in people with affective disorders, psychosis, and personality disorders.

Drug interactions

Some drugs, such as MDMA, can also cause extreme thirst, which may lead to over-drinking water.

Some diuretics and vasopressors can also increase a person’s risk of hyponatremia.

It is difficult to consume too much water by accident. However, in rare instances, it can lead to fatal complications.

People at risk of death from water intoxication tend to be participating in endurance sporting events, military training, or other high-exertion undertakings.

Overhydration and water intoxication happen when a person drinks more water than their kidneys can get rid of via urine. The amount of water is not the only factor — time also plays a role.

According to figures quoted in a 2013 study, the kidneys can eliminate about 20–28 liters of water a day, but they can remove no more than 0.8 to 1.0 liters every hour.

To avoid hyponatremia, it is important not to outpace the kidneys by drinking more water than they can eliminate.

The authors of the study report that hyponatremia symptoms can develop if a person drinks 3–4 liters of water in a short period. However, they do not give a specific time estimate.

According to the Centers for Disease Control and Prevention (CDC), there are no official guidelines about how much water a person needs to drink each day.

The right amount differs, depending on factors such as body weight, level of physical activity, climate, and whether they are chestfeeding.

Read more about daily water intake recommendations here.

Drinking too much water can lead to water intoxication. This is rare and tends to develop among endurance athletes and soldiers.

There are no official guidelines about how much water to drink. To avoid water intoxication, some sources recommend drinking no more than 0.8 to 1.0 liters of water per hour.