Overhydration is a serious, possibly fatal, problem within the brain caused when the normal balance of electrolytes in the body is altered due to an excessive amount of water being consumed over a short time period. This overconsumption of water is also sometimes called water intoxication, water excess, hyper-hydration, or water poisoning. Normal hydration is important in the area of fitness and exercise because a proper water level within the body is an essential part of a healthy lifestyle. During strenuous physical activities, the body's water level can drastically change, leading to health issues.


The consumption of water is a necessary function of life. Humans must drink water on a regular basis in order to stay alive. In fact, humans can live for only about a week without water, even less if they are in a hot, dry environment. Hydration is the process by which humans take in and maintain a steady level of water in their tissues and organs down to the cellular level. During this process, adequate fluid levels in the body are in balance, what is called homeostasis. However, it is possible for people to become overhydrated from excessive fluid intake.

Too much water over a short period can be potentially dangerous, to the point of causing coma or death. Under normal circumstances, it is very unlikely that someone will accidently drink too much water. Usually, cases of overhydration occur when infants are fed too many fluids, adults have medical or mental problems related to water consumption, or people consume huge amounts of water while trying to stay hydrated during intense periods of physical activity or exercise. For instance, when marathon runners or bicyclists are competing during very hot conditions, they will drink large amount of water to replenish fluids lost to perspiration. The normal percentage of water that is daily replaced in healthy adults is between 5% and 10%. That percentage dramatically increases during physical activities and and/or during very hot climatic conditions. Thus, people participating in strenuous activities try to replenish those fluids lost through sweating. However, sometimes they drink too much water—much more than they actually lose.

In addition, cases have been documented where contests were held in which people won money or prizes for the most water drunk. For instance, in January 2007, Jennifer Strange, of Rancho Cordova, California, was found dead after participating in a radio contest called “Hold Your Wee for a Wii,” in which the prize was a Nintendo Wii video game system. She drank a large amount of water while not urinating, and died from overhydration. Such contests are dangerous and should not be held due to the extreme danger involved in such actions.

When overhydration happens the normal balance of electrolytes in the body is altered. Electrolytes are chemical compounds that help to control bodily fluid levels that allow for the proper transmission of nerve signals throughout the body. When too much water and not enough electrolytes (especially sodium) are in the body, then the cells in the brain try to swell. However, they cannot expand because the brain is encased within a rigid skull called the cranium. This causes intracranial pressure, the first sign of overhydration. Other later symptoms of overhydration include seizures and, in some rare cases, death. Overhydration usually leads to hyponatremia, a condition in which the level of sodium, one type of electrolyte, in the blood plasma is too low.


Overhydration can occur in anyone. However, it is more commonly found in infants under the age of six months. Oftentimes infants may become overhydrated when drinking several bottles of water in a day or from drinking milk formula that has been diluted too much.

Athletes and others that exercise strenuously can also become afflicted with overhydration if they drink much more water than they lose to perspiration. When athletes sweat heavily, they lose both water and electrolytes. If water is consumed in large amounts during and after such strenuous exercise, then the balance of electrolytes can be altered. In such circumstances, people who drink liquids that contain electrolytes are less likely to become overhydrated, but are still at risk due to the excessive amount of liquid introduced into the body.

Other groups of people at increased risk for overhydration include those people who use excessive amount of alcohol or drugs, have medical problems such as diarrheal diseases, and have certain psychological disorders.

Causes and symptoms


Causes for overhydration include:

Substances in the body that are able to conduct electricity. They are essential in the normal functioning of body cells and organs.
A condition characterized by severe inflammation of the gastrointestinal tract, usually involving both the small intestines and the stomach, with main symptoms of diarrhea and vomiting.
Homeostasis (water)—
A condition of adequate fluid level in the body in which fluid loss and fluid intake are equally matched and sodium levels are within normal range.
An abnormally low level of sodium in blood plasma.
Psychogenic polydipsia—
A psychiatric disorder in which patients consume excessive amounts of water, sometimes going to great lengths to obtain it from any source possible.

Various symptoms that initially appear during overhydration include:

Later symptoms that occur after the initial symptoms of overhydration include:

In the later stages of overhydration the following more dangerous symptoms occur:

Finally, coma and death can occur.


A medical professional will analyze the symptoms of the patient, along with his/her past history over the past few days to partially determine whether overhydration is the cause. However, symptoms of overhydration occur in many medical disorders, so this process only narrows down the exact problem. Consequently, the doctor will also use blood and urine tests to completely and properly diagnose overhydration.


Mild cases of overhydration can be generally alleviated by limiting fluid intake. However, in serious cases diuretics may be prescribed to quickly increase urination. In the most dangerous of overhydration cases, fluids to restore a normal balance of electrolytes will be administered quickly. After about half of the fluids have been introduced into the body, the rate of absorption is reduced to a more moderate rate.


Mild overhydration has a favorable outcome. However, moderate to serious cases can be fatal if not properly and quickly treated. In most circumstances, death is rarely the final outcome.


Never drink excessively large amounts of water over a short time period. The American College of Sports Medicine (ACSM) recommended in 2007 that proper hydration during exercise should be geared personally to each athlete rather than strictly associated with general guidelines. The ACSM states: “The goal of drinking during exercise is to prevent excessive (more than 2% body weight loss from water deficit) dehydration and excessive changes in electrolyte balance to avert compromised performance.”


Because there is considerable variability in sweating rates and sweat electrolyte content between individuals, customized fluid replacement programs are recommended.” The ACSM added in 2008: “Drink fluids before exercise and periodically during exercise, instead of practicing rapid fluid replacement in the middle of exercise. Drinking at intervals will provide more adequate hydration and urine production.”

To prevent overhydration, never drink excessive amounts of water. A healthy adult would have to drink over 2 gal (7.6 L) of water in a day to develop overhydration. The medical community suggests that people drink at least 0.25–0.5 gal (1–2 L) of water per day. Specifically, the Food and Nutrition Board of the Institute of Medicine (IOM) recommended in 2004 (and is still accurate as of February 2011) that relatively inactive adult men take in about 125 oz (3.7 L, about 15 cups) of fluids daily and that women take in about 91 oz. (2.7 L, about 10 cups) to replace lost water. These recommendations are for total fluid intake from both beverages and food.

The World Health Organization (WHO) recommendations are slightly different: 98 oz. (2.9 L) for men and 74 oz. (2.2 L) for women (162 oz. [4.8 L] for pregnant women). Highly active adults and those living in very warm climates need more fluid; WHO recommends 152 oz. (4.5 L) per day for both men and women in these conditions. This amount may also vary depending on body mass. Overhydration will occur only at levels much higher than this amount.

See also Water intoxication .



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

American Council on Exercise, 4851 Paramount Dr., San Diego, CA, 92123, (858) 576-6500, (888) 825-3636, Fax: (858) 576-6564, support@acefitness.org, http://www.fitness.gov .

National Coalition for Promoting Physical Activity, 1150 Connecticut Ave. NW, Ste. 300, Washington, DC, 20036, (202) 454-7521, ayanna@ncppa.org, http://www.ncppa.org .

National Strength and Conditioning Association, 1885 Bob Johnson Dr., Colorado Springs, CO, 80906, (719) 632-6722, (800) 815-6826, Fax: (719) 632-6367, nsca@nsca.com, https://www.nsca.com .

President's Council on Fitness, Sports & Nutrition, 1101 Wootton Pkwy., Ste. 560, Rockville, MD, 20852, (240) 276-9567, Fax: (240) 276-9860, fitness@hhs.gov, http://www.presidentschallenge.org .

SHAPE America, 1900 Association Dr., Reston, VA, 20191-1598, (800) 213-7193, Fax: (703) 476-9527, http://www.shapeamerica.org .

William A. Atkins, BB, BS, MBA

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