Water Intoxication: Too Much of a Good Thing is a Bad Thing

Drinking water
Written by Sean Nelson

Water is the most essential chemical sustaining human life, and it is a well-known fact that drinking plenty of it is great for maintaining physical health. But in addition to water, the human body needs many other minerals and electrolytes, such as sodium, to function properly.

When water and these other minerals become imbalanced, a dangerous condition known as water intoxication can occur. Here, we will review some of the causes, signs and symptoms of water intoxication to help you recognize this dangerous condition in yourself or others.

When considering proper water intake, in most cases the danger is dehydration. Suffering dangerous symptoms from too little water intake is far more common than cases in which there is excessive water intake. While it is exceedingly rare, however, water intoxication is a real threat especially in people in certain situations or conditions.

See also: Water Poisoning: Treatment & Prevention

The average human body is made up of approximately 66 percent water. This physiologic water level is constantly in a state of flux as water is lost through sweat, respiration, and urination. Each day, 1 to 2 liters of water are lost from the body just as a result of breathing.

The amount of water you need to intake through food and beverage varies from person to person depending on climate, body size and activity levels. The commonly repeated adage of “Drink eight, eight-ounce glasses of water each day” can actually be an unhealthy quantity of water for many people who do not need that much water.

The Physiology of Water Intoxication

Much of human physiology is dictated by a homeostatic balance between chemical levels. Minerals such as sodium and potassium regulate cellular function in the body and allow it to function. One of these important balances is the sodium-water balance.

Dehydration can also be thought of as hypernatremia, or excessive salt in the cells. The opposite, hyponatremia, is when there is too much water in the water-sodium ratio. In quantitative terms, hyponatremia is defined by the blood sodium concentration falling below 135 millimoles per liter.

Levels of sodium and water in the blood are regulated by the kidneys, which function to filter out blood. However, there is a maximum rate at which kidneys are able to filter blood.

In a healthy adult, a healthy kidney at rest can excrete about 0.25 gallons of water an hour. However, water intoxication is not simply caused by drinking excessive amounts of water. The effects of this condition can be compounded by other factors such as the hormone vasopressin.

Vasopressin is an antidiuretic hormone that is produced by the hypothalamus and secreted into the blood stream by the posterior pituitary gland. Vasopressin, which assists in water retention, is secreted in greater quantities during physical stress such as endurance events.

While the kidneys can excrete 0.25 gallons of water an hour during a normal physiological state, high vasopressin secretion can reduce this to 100 milliliters per hour. With that reduced volume of water being filtered through the kidneys, excessive water intake can be even more dangerous than usual.

Signs and Symptoms of Water Intoxication

Hyponatremia is dangerous because it can lead to edema, or swelling of the cells. When there is excessive water in the blood stream that can’t be filtered by the kidneys quickly enough, this water passes into the cells and exceeds the sodium-water balance.

While cells in most tissues can withstand some swelling, the real danger occurs when brain cells, or neurons, undergo swelling. Even mild cerebral edema can cause health issues that are noticeable almost immediately.

Signs of water intoxication are generally due to this cerebral edema. Some early signs of increased intracranial pressure due to excessive water in the neurons include headache, changes in personality, changes in behavior, confusion, irritability, and drowsiness.

Physical signs and symptoms can be manifested as difficulty breathing during exertion, muscle weakness and pain, twitching, cramping, dilated pupils, cyanosis, hypothermia, nausea, vomiting and thirst. Bradycardia and a widened pulse pressure can also be experienced.

It can be difficult to differentiate between water intoxication and dehydration at times because some of the warning signs of water intoxication are similar to those experienced by patients with heat stroke. This includes feeling hot, having a headache, nausea, diarrhea or vomiting.

Because the two conditions have such similar signs and symptoms, it is very important to consider fluid intake and whether too much water, rather than too little, is actually the cause of illness. Deciding a person with water intoxication is actually dehydrated and attempting to give him or her more water can only exacerbate the problem.

Symptoms of advanced water intoxication include seizures, coma, respiratory arrest, brain stem herniation, and death. Even if hyponatremia is caught and treated, there can be long term conditions that result from the brain damage.

Mental retardation, hearing loss, and other neurological complications like changes in gait can occur. A patient experiencing water intoxication can be treated with diuretics or vasopressin receptor antagonists. Should you or someone you know become hyponatremic, calling 911 can save a life.

Risk Factors for Water Intoxication

Some people are more likely than others to experience water intoxication. Infants have a lower body mass and are more susceptible to excessive intake of fluids. Patients on intravenous fluids are carefully monitored for blood levels of minerals and water to keep everything in check.

Some people with certain psychological conditions can have a compulsion to drink dangerous amounts of water. One of the most common ways that normally healthy adults can become hyponatremic, however, is through overexertion in exercise and endurance events. There have been multiple documented cases of people who have taken the drug MDMA dying of water intoxication.

The overexertion caused by partying while under the influence causes them to drink excessive water and possibly die. “Water drinking challenges” also pose a threat. A woman died in a radio station contest by drinking too much water without urinating.

Water drinking challenges can be especially popular among teenagers, so if someone you know is planning to participate in one make sure they are aware of the dangers associated with consuming more water than his or her body can handle. Water can seem like the most harmless of substances but everything in excess can be dangerous.

Endurance events such as marathons can also result in water intoxication. In a study of runners in the 2002 Boston Marathon, it was found that thirteen percent of people finished the race at least mildly hyponatremic. Of course, drinking plenty of water during endurance events including long distance hiking or biking is essential to peak performance.

Too much, especially in a stressed physical state where the body is secreting large quantities of vasopressin, can be deadly. Other risk factors include a low body weight, fasting or starvation, and diabetes mellitus that is poorly controlled. Water retention can also occur with certain drugs, kidney disorders, heart failure, cirrhosis, Addison’s disease, or excessive secretion of the antidiuretic hormone SIADH.

Monitoring and Treating Water Intoxication

If you know that you are experiencing water intoxication, get emergency medical help immediately. Medical intervention includes the intravenous administration of concentrated salt to help with homeostasis and drawing water out of dangerously swollen cells.

It can be difficult to measure water intake and output especially in sweat and respiration. Levels of hydration can be qualitatively judged by looking at urine color. If urine is completely clear, it might be a sign of too much water intake. Most doctors advise that water intoxication can be avoided by drinking when you feel thirsty and stopping when you are satiated. For more guidelines on how to prevent overhydration, see this link.

Sometimes sports drinks such as Gatorade can be safer than water because they contain electrolytes. But water intoxication can still happen with too much intake of any liquid, whether it be water, Gatorade or beer. When paired with a diet lacking sodium, excessive intake of beer can cause hyponatremia as well.

A Step-by-Step Guide for Preventing, Recognizing and Treating Water Intoxication

Be aware of situations in which you might overhydrate. Endurance events such as marathons or other times when overexertion is possible are examples.

  1. Drink when you are thirsty. It can be difficult to monitor exact input and output levels of water, but thirst can alert you to when you need to drink more water.
  2. Monitor urine color. Dark urine can indicate dehydration, while clear urine could indicate too much water intake.
  3. Watch for early signs of water intoxication including confusion, changes in personality and behavior, headache, or cramping.
  4. If water intoxication is suspected, seek medical attention as soon as possible. Try to consume something salty to help balance out the salt-water balance. A diuretic can also help with excreting excess water from the body.
  5. Even if symptoms subside, monitor the patient or yourself for advanced symptoms of water intoxication that could appear, including neurologic changes, coma, seizures, or respiratory issues.


Although staying properly hydrated is essential, there can be too much of a good thing. Human physiology is dictated by balances, including the one between sodium and water. Being aware of signs and symptoms as well as risk factors for water intoxication can help you to identify when someone has ingested more water than is healthy for his or her body.

Once again, the most important advice to avoid water intoxication is “drink to your thirst.” The human body usually does a good job of communicating its needs for food and liquid. With the exception of some psychological conditions, if you crave salt or water, there is probably a good reason. Have you ever had an experience involving overhydration?

For more tips on how to stay properly hydrated throughout the day, check out our article on this topic.

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Sean Nelson

Sean was backpacking since he was 7. He was born close to the RMNP and his father was a ranger, so life surrounded by mountains and wildlife is a norm for Colorado. He likes to explore, but prefers to stay in USA. In his opinion, there are too many trails and options in US to go abroad.