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Water intoxication: If you drink too much water, what happens?

All of your cells and organs require water for proper functioning. Excessive consumption of water can, however, lead to water poisoning.

In certain instances, this has been considered to be fatal.

Water intoxication


Water intoxication, also known as water poisoning, is the disturbance of brain activity due to consuming too much water (1).

Drinking lots of water makes your blood more watery.

This water, particularly sodium, can dilute the electrolytes in your blood. This is called hyponatremia when sodium levels fall below 135 mmol / L.

Sodium helps to regulate fluids between the inner and outer cells.

Due to excess water intake, as sodium levels decrease, fluids migrate from the outside to the inside of cells, causing them to swell (2).

This can cause harmful and potentially life-threatening results when occurring in brain cells.

Bottom line: Drinking too much water causes water intoxication. The extra water dilutes sodium levels in the blood and allows fluids to pass inside cells, which then swell.

Dangers of too much water

Water intoxication results from the swelling of cells.

Pressure within the skull increases as brain cells swell. This pressure triggers the first signs of water intoxication, such as:

Severe cases can produce more serious symptoms, such as:

  • Increased blood pressure.
  • Confusion.
  • Double vision.
  • Drowsiness.
  • Difficulty breathing.
  • Muscle weakness and cramping.
  • Inability to identify sensory information.

Excess accumulation of fluid in the brain is called the cerebral edema which can affect the center of the brain and cause dysfunction of the central nervous system.

In extreme cases, water poisoning can cause seizures, damage to the brain, coma and even death (1).

Bottom line: Drinking too much water raises the pressure inside in the skull. This may cause different symptoms and, in extreme cases, may even be fatal.

Can it be fatal?

By mistake, drinking too much water is very difficult, but cases of death have been recorded because of this condition.

In soldiers multiple cases of water intoxication have been recorded (34).

One study dealt with 17 soldiers who developed hyponatremia due to excess water intake. A levels of sodium in the blood ranged from 115 to 130 mmol / L, but the typical range is 135 to 145 mmol / L (4).

Another study explained how the hyponatremia and cerebral edema caused three soldiers to die. Such deaths were linked in just a few hours to drinking 2.5-5.6 gallons (10-20 liters) of water (5).

Hyponatremia signs can be misinterpreted as dehydration ones. One soldier, misdiagnosed as suffering from dehydration and heat stroke, died as a result of excessive oral hydration from water intoxication (3).

Water poisoning also occurs during sports, in particular during endurance sports. In such activities overhydration is common as a means of preventing dehydration.

Hyponatremia, for this reason, frequently occurs during major sporting events (67).

13 percent of participants had signs of hyponatremia at the 2002 Boston Marathon. Critical hyponatremia was seen at 0.06 per cent with sodium levels below 120 mmol / L (8).

Unfortunately, several cases of water intoxication have resulted in deaths at such sporting events.

After a marathon one event involved a driver. Tests showed its sodium level was below 130 mmol / L. He developed hydrocephalus and herniation of the brain stem which led to his death (9).

In psychiatric patients, in particular schizophrenics, too much water consumption can also occur (101112).

One study of 27 schizophrenics who died young has shown that five of them died from self-induced water poisoning (13).

Bottom line: Water intoxication is most common among soldiers, endurance athletes and patients with schizophrenia.

How much is too much?

Over-hydration and water intoxication occurs when you are consuming more water than your kidneys can get rid of by urine.

Drinking enough water

But the water quantity is not the sole factor. How long it takes you to drink water counts as well.

If you drink a lot of water in a short period of time, you have a greater chance of developing water intoxication. The risk is smaller if you drink the same amount over a much longer period of time.

Symptoms of hyponatremia that occur in a short period of time from as little as 0.8-1 gallons (3-4 litres) of water (14).

Your kidneys that remove about 5.3-7.4 gallons (20-28 liters) of water per day, but they can’t get rid of more than 27-33 ounces (0.8-1.0 liters) an hour (1415).

So you can not drink more than 27-33 ounces (0.8-1.0 liters) of water an hour on average to prevent symptoms of hyponatremia (14).

Many recorded cases of water intoxication are the result of consuming large quantities of water in a short time span.

One study, for example, describes soldiers who developed symptoms after drinking half a gallon (1.8 liters or more) of water every hour (4).

Another study shows the production of just a few hours of hyponatremia with a water intake of 2,5-5,6 gallons, or 10-20 liters (5).

A case of water intoxication and sustained hyponatremia also occurred in a healthy adult, 22-year-old inmate after drinking 1.5 gallons (6 liters) of water in 3 hours (1).

Finally, a 9-year-old girl who consumed almost a gallon (3.6 liters in total) of water within 1-2 hours experienced water intoxication (14).

Bottom line: The kidneys can excrete as much as 7 gallons (28 liters) of fluid per day. They can’t excrete more than 1 liter per hour though. And it is not a good idea to drink more than this.

How much water do you need?

There’s no precise number on how much water you need to actually drink a day. It’s different for every single person.

Consider your body weight, physical activity level and the environment to decide how much you need.

The Institute of Medicine (IOM) reports that for men the sufficient consumption of water per day is 125 ounces (3.7 liters), while for women it is 91 ounces (2.7 litres).

Such guidelines however include beverage and food water (16).

Some people are still following the 8 x 8 law, which recommends eight 8-ounce glasses of water a day. This law, however, is largely arbitrary, and is not based on research (1718).

Listening to your body and drinking when you are thirsty is a healthy rule of thumb. This should be adequate to maintain good levels of hydration.

Trusting in thirst alone can not work for everyone, though. Athletes, older adults and women who are pregnant may need to drink some extra water every day.

Chukwuebuka Martins

Chukwuebuka Martins is a writer, researcher, and health enthusiast who specializes in human physiology. He takes great pleasure in penning informative articles on many aspects of physical wellness, which he then thoroughly enjoys sharing to the general public.