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 are general — 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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A person may experience water intoxication if they drink too much water.

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.

Bottom line: Water intoxication results from drinking too much water. The excess water dilutes sodium in the blood and causes fluids to move inside cells, causing them to swell.

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.

Bottom line: Drinking too much water can increase the pressure inside the skull. This can cause various symptoms and, in severe cases, become fatal.

Water intoxication is rare, and it is very difficult to consume too much water by accident. However, it can happen — there have been numerous medical reports of death due to excessive water intake.

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 is particularly common among 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 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.

Instances of water intoxication at these events have resulted in death. One case involved a runner who had collapsed after a marathon.

Because he was improperly rehydrated, his sodium levels fell below 130 mmol/l. The runner then developed water on the brain, known as hydrocephalus, and a hernia in his brain stem, which caused his death.

Military training

One medical report described 17 soldiers who developed hyponatremia after drinking too much water during training. Their blood sodium levels were 115–130 mmol/l, while the normal range is 135–145 mmol/l.

According to another report, three soldiers died due to hyponatremia and cerebral edema. These deaths were associated with drinking more than 5 liters of water in just a few hours.

The symptoms of hyponatremia can be misinterpreted as those of dehydration. According to one report, a soldier who received an incorrect diagnosis of dehydration and heat stroke died from water intoxication as a result of rehydration efforts.

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.

Bottom line: Water intoxication can be life threatening, and it is most common among soldiers in training, endurance athletes, and people with schizophrenia.

It is difficult to consume too much water by accident. However, it can happen, and there have been numerous reports of death due to excess water intake.

People at risk of death from water intoxication tend to be participating in endurance sporting events or military training. A person who is doing neither is unlikely to die from drinking too much water.

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, though they do not give a specific time estimate.

According to one case report, soldiers developed symptoms after consuming at least 2 quarts (1.9 liters) of water per hour.

Another report describes the development of hyponatremia after drinking more than 5 liters in a few hours.

Water intoxication and prolonged hyponatremia also occurred in an otherwise healthy 22-year-old prisoner who drank 6 liters of water in 3 hours.

Finally, according to one report, a 9-year-old girl developed water intoxication after consuming 3.6 liters of water in 1–2 hours.

Bottom line: The kidneys can remove 20–28 liters of water per day, but they cannot excrete more than 0.8 to 1.0 liters per hour. Drinking more than this can be harmful.

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, the climate, and whether they are breastfeeding.

In 2004, The National Academy of Medicine recommended that women aged 19–30 consume around 2.7 liters per day and men of the same age around 3.7 liters per day.

Some people still follow the 8×8 rule, which recommends drinking eight 8-ounce glasses of water per day. However, this was not based on research.

Relying on thirst may not work for everyone. Athletes, older adults, and pregnant women, for example, may need to drink more water each day.

To estimate the right amount, it can help to consider calories. If a person needs 2,000 calories per day, they should also consume 2,000 milliliters of water per day.

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.