Water Intoxication


It is often recommended that people drink eight glasses of water each day. However, too much water suddenly consumed can be dangerous. Excess water— what is called water intoxication—is a serious and potentially deadly disorder that occurs when an abnormally high amount of water is consumed or when electrolytes are not properly replenished, even though water is consumed, during intense exercise. Such situations can cause serious disturbances in brain functions. Water intoxication is also commonly called water poisoning, overhydration, or hyperhydation.


When too much water is consumed, the kidneys are unable to properly process such large amounts of water, salts, and other solutes. Consequently, an imbalance of electrolytes occurs. Electrolytes are any substance containing free ions that makes it electrically conductive— either with an excess (negative charge) or deficit (positive charge) of electrons.

When an electrolyte imbalance occurs, the kidneys process as much fluids as they can; however, the excess fluids are forced into the blood, eventually entering the cells of the body. Then, the cells expand to accommodate the excessive fluids. In essence, the cells become waterlogged.

When too much water is consumed, a lower concentration of electrolytes, especially sodium, are contained on the outside of cells compared to the inside. To correct this imbalance, fluid is moved inside the cells, causing them to enlarge. At the same time, electrolytes are transferred from inside the cells to the outside, to balance their concentration. As this occurs, more water is transfer inside the cell, again trying to maintain appropriate electrolyte balance. Cells outside of the brain continue this balancing act, swelling larger as more water enters. They are able to stretch safely because they are contained within flexible tissues. The extra water does not adversely affect them.

However, neurons in the brain are not able to swell safely because they are contained within a rigid skull. Thus, adverse consequences occur because as the cells swell in the brain, the brain itself begins to swell, what is called brain edema. This condition leads to increased pressure on the brain, causing the first signs of a problem including headaches, irritability, and drowsiness. As the problem grows, further symptoms develop, including difficulties in breathing, nausea, and vomiting. When this potentially deadly state occurs, the brain is not receiving an adequate amount of blood because the enlarged size of the cells prevents its flow. Pressure to the brain stem begins to cause the nervous system to fail, eventually leading to brain damage, respiratory arrest, seizures, brain stem herniation, coma, and even death.

Water intoxication can occur in athletes, especially when they exercise strenuously. A study published in the August 2004 issue of the British Journal of Sports Medicine is entitled “The Dipsomania of Great Distance: Water Intoxication in an Ironman Triathlete.” The South African authors studied 371 athletes after finishing the 140-mile (226-kilometer) South African Ironman Triathlon. The most weight gained during the competition was approximately 7.9 pounds (3.6 kilograms). This athlete also developed signs of hyponatraemia. During his recovery, the athlete excreted 1.2 gallons (4.6 liters) of urine. The authors stated, “This case report again confirms that symptomatic hyponatraemia is caused by considerable fluid overload independent of appreciable NaCl [sodium chloride, also called salt] losses. Hence, prevention of the condition requires that athletes be warned not to drink excessively large volumes of fluid (dipsomania) during very prolonged exercise. This case report also shows that there is a delayed diuresis in this condition and that it is not caused by renal failure.”

Relating to excess fluids.
Any ion in cells, blood, or other organic substance, whose purpose is to control fluid levels in the body.
Poisoning by ingestion of a drug, toxic substance, or other such material (such as water).
Within the skull.
A pair of organs in the abdomen of vertebrates that filter wastes, which are then excreted as urine from the body.
A unit within the International System of Units (SI) that measures the amount of a chemical substance, equaling about 6.02214 x 1023 molecules of that substance.
Extreme thirst.
A substance dissolved in another substance.


Healthy people normally do not get water intoxication when nutritionally balanced foods and drinks are consumed each day. However, several groups of people are more at risk than are others. Water intoxication is most frequently found in infants six months of age or younger, and sometimes in athletes.

Infants and children with inflammation of the gastrointestinal tract, such as from influenza (flu), are at increased risk from water intoxication because a large electrolyte imbalance can quickly result when vomiting and diarrhea occurs. Infants under the age of one year are also at heightened risk when they have a lower than normal body mass because such a small weight makes it quite easy to take in a relatively large amount of water in a small amount of time.

Any person is at higher risk from water intoxication when conditions cause excess sweating during physical activities or exercising. This is partially because water alone will not replenish needed nutrients into the body. During and after these times, is it extremely important to drink and eat nutritious substances to maintain a balance of electrolytes in the body.

People with the mental condition called psychogenic polydispia are also at heightened risk of water intoxication. The disorder is characterized by a patient unable to stop drinking water due to a compulsion to drinking water or as a result from taking antipsychotic medications used to treat various other mental disorders.

Causes and symptoms


Water intoxication occurs usually when someone drinks large amounts of water or when intense exercise has been completed and water was been drunk but without proper replenishment of electrolytes.

For athletes, hyponatremia, a type of water intoxication, can often occur. Hyponatremia is a condition in which an electrolyte imbalance occurs with the chemical element of sodium. Sodium concentration in the blood becomes lower than normal when excessive water being consumed. Specifically, the blood sodium concentration drops below 135 millimoles per liter, which is about 0.4 ounces per gallon. A normal concentration in the body is from 135–145 millimoles per liter. Water intoxication is the result of severe cases of hyponatremia.


The initial symptoms of water intoxication include those that are similar to psychosis, including inappropriate behaviors, confusion, delusions, hallucinations, and disorientation. Associated symptoms include headache, fatigue, nausea, vomiting, and frequent urination. These symptoms can progress to acute delirium, seizures, coma, and even death.


Water intoxication should be diagnosed as early as possible to counter its effects in the body. However, in many cases, due to incomplete research and understanding into water intoxication, the problem is not properly diagnosed in its early stages even when clear signs of confusion, disorientation, nausea, and vomiting are present.



When mild cases of water intoxication occur, restriction of water intake is usually the only necessary step. However, in moderate to serious cases, medical professionals are likely to prescribe diuretics in order to increase the rate of urination. Vasopressin receptor antagonists—any substances that interfere with actions at the vasopressin receptors that bind with vasopressin, a hormone that controls the re-absorption of molecules in the kidneys—may also be prescribed.


An early diagnosis and treatment for water intoxication are crucial to prevent seizures, coma, and possibly death.


Restriction of water consumption can prevent water intoxication. Under normal circumstances, people should drink at least 1.0–2.1 quarts (1–2 liters) of water per day or about 34–68 fluid cups (4–8 glasses). Water intoxication occurs only when such levels have been far exceeded.

Healthy kidneys can excrete, under normal circumstances, about 27–34 fluid ounces (800–1,000 milliliters, or 0.8–1.0 liters) of fluids per hour without gaining additional water inside the body. However, strenuous exercise can reduce the amount of fluids that can be expelled by the kidneys. The capacity of kidney excretion can reach as low as 100 milliliters per hour. Therefore, for example, drinking 800 milliliters of water per hour (even when sweating profusely) can lead to dangerous conditions within the body.

See also Overhydration .



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Noakes, T. D., K. Sharwood, M. Collins, and D. R. Perkins. “The Dipsomania of Great Distance: Water Intoxication in an Ironman Triathlete.” British Journal of Sports Medicine 38, no. 4 (August 2004): E16. http://www.ncbi.nlm.nih.gov/pubmed/15273209 (accessed January 26, 2017).


American College of Sports Medicine, 401 W Michigan St., Indianapolis, IN, 46202-3233, (317) 637-9200, Fax: (317) 634-7817, http://www.acsm.org .

William A. Atkins, BB, BS, MBA

  This information is not a tool for self-diagnosis or a substitute for professional care.