How many ounces of water is considered water poisoning?

November 24, 2025 •

4 min read

While drinking too much water can be risky, it's a rare and often misunderstood condition. Water intoxication, also known as hyponatremia, occurs when a person consumes more water than their kidneys can handle in a short period, diluting the body's sodium levels.

Quick Summary

Water poisoning, or hyponatremia, is caused by excessive water intake overwhelming the kidneys, diluting sodium levels. The amount of water that causes this varies, but drinking more than 32 ounces per hour is generally too much for healthy adults. Severe cases can lead to brain swelling, seizures, and death.

Key Points

Hourly Limit: Healthy kidneys can process about 27-33 ounces of water per hour, and exceeding this amount significantly can increase the risk of water poisoning.
Cause of Poisoning: Water poisoning, or hyponatremia, is caused by overhydration diluting the blood's sodium levels, which is crucial for cellular fluid balance.
Brain Swelling: When sodium levels drop due to excessive water intake, brain cells can swell, leading to symptoms like confusion, headaches, seizures, and in severe cases, coma or death.
Listen to Thirst and Urine Color: The most effective prevention methods are drinking only when thirsty and monitoring urine color; clear urine is an indicator of overhydration.
Risk Factors: Endurance athletes, individuals with certain medical conditions (like kidney disease), infants, and people on specific medications are at higher risk.
Electrolyte Balance: For prolonged exercise, supplementing with electrolyte-containing sports drinks is recommended to help maintain proper sodium levels.
Consult a Professional: If you have underlying health issues or questions about your hydration needs, consulting a healthcare provider is the safest approach.

Understanding Water Poisoning (Hyponatremia)

Water poisoning, or hyponatremia, is a serious condition that results from overhydration. When you drink excessive amounts of water in a short period, your kidneys become overwhelmed and cannot excrete the fluid fast enough. This causes the sodium levels in your blood to become dangerously diluted. Sodium is a vital electrolyte that helps maintain fluid balance both inside and outside your body's cells. When sodium levels drop, water moves into your cells, causing them to swell. This swelling is especially dangerous in the brain, where it can cause significant pressure and interfere with neurological function.

How Many Ounces Per Hour is Too Much?

There is no single amount of water that guarantees water poisoning, as it depends on individual factors like age, health, and activity level. However, research indicates a general guideline for healthy adults. The kidneys can typically process and excrete about 0.8 to 1.0 liters (around 27 to 33 ounces) of water per hour. Drinking significantly more than this hourly limit for several hours can increase the risk of developing hyponatremia. In fact, some sources suggest that consuming more than 32 ounces (about 1 liter) per hour is likely too much. For example, in one tragic case, a woman died after consuming six liters of water (over 200 ounces) during a drinking contest in just three hours.

Factors Influencing Your Risk of Water Poisoning

Beyond the sheer quantity of water consumed, several other factors can increase a person's risk of water poisoning:

Intense Exercise: Endurance athletes, such as marathon runners or military personnel in training, are at higher risk because they sweat out electrolytes, and over-replenishing with only plain water further dilutes their sodium.
Underlying Medical Conditions: Certain health issues can compromise the kidneys' ability to excrete water effectively. These include heart, liver, and kidney diseases, and the Syndrome of Inappropriate Antidiuretic Hormone (SIADH).
Small Body Size: Infants and children are particularly vulnerable because of their smaller body mass and less mature kidneys. Health experts advise against giving infants under one year old plain water unless directed by a doctor.
Medications and Drugs: Certain medications, such as some antidepressants, diuretics, and antipsychotics, can increase thirst or interfere with water and sodium balance. The recreational drug MDMA (ecstasy) also elevates risk.
Psychological Disorders: Conditions like psychogenic polydipsia can cause a compulsive desire to drink excessive amounts of water.

Symptoms of Water Intoxication

Symptoms can range from mild to severe and may be confused with other conditions. It is critical to recognize the signs, especially if someone has consumed a large amount of water in a short time. Early signs include:

Headache
Nausea and vomiting
Bloating
Fatigue or drowsiness

As the condition progresses, more severe symptoms can emerge:

Muscle weakness, cramping, or spasms
Confusion, irritability, or altered mental status
Seizures
Coma or death in severe cases

How to Prevent Water Poisoning

Preventing overhydration is often as simple as listening to your body's cues. Here are some preventative strategies:

Drink to Thirst: Your body has a natural thirst mechanism. Drink when you feel thirsty, and stop once your thirst is quenched.
Monitor Urine Color: Your urine color can be a good indicator of hydration status. A pale yellow color, like lemonade, is ideal. If your urine is clear, it's a sign that you are likely overhydrated and should hold off on drinking more fluids.
Replenish Electrolytes During Intense Exercise: If you are engaging in prolonged, intense physical activity where you sweat heavily, consider using a sports drink with electrolytes to help balance your sodium levels.
Space Out Your Water Intake: Avoid chugging large amounts of water in a short time. Spread your hydration throughout the day.
Consult a Professional: If you have a medical condition affecting kidney function or are on certain medications, talk to a doctor about safe fluid intake levels.

Water Intoxication vs. Dehydration


Feature	Water Intoxication (Hyponatremia)	Dehydration
Cause	Excessive water intake, causing low blood sodium.	Inadequate fluid intake, causing elevated blood sodium and concentration.
Primary Electrolyte Imbalance	Sodium levels are too low.	Sodium levels are too high or normal, but total body water is low.
Fluid Balance	Fluid moves into cells, causing them to swell.	Cells shrivel as fluid moves out of them.
Urine Appearance	Clear or colorless and frequent.	Dark yellow and infrequent.
Mental State	Confusion, restlessness, or irritability.	Confusion, sluggishness, or extreme thirst.
Muscle Symptoms	Weakness, cramps, or spasms.	Weakness and fatigue.
Weight	May increase due to fluid retention.	May decrease due to fluid loss.

Conclusion

While water is essential for health, excessive intake in a short period can lead to a dangerous condition known as water poisoning, or hyponatremia. The risk of developing this is highly individual, but a good rule of thumb is to avoid drinking more than 32 ounces per hour, especially during strenuous activity. The body's natural thirst mechanism and urine color are reliable indicators of hydration needs. By understanding the causes, symptoms, and risk factors, you can practice safe hydration and prevent this potentially life-threatening condition. Always listen to your body and consult a healthcare professional if you have concerns about your water intake or suspect overhydration. For further guidance on maintaining proper electrolyte balance, especially during exercise, it is important to remember the crucial role of sodium alongside fluid replacement. The Cleveland Clinic provides extensive resources on water intoxication and prevention.

Frequently Asked Questions

Overhydration is the general state of having too much water in the body, while water intoxication is the specific medical condition caused by the resulting dangerously low sodium levels, known as hyponatremia.

It is extremely rare for a healthy person with normal kidney function to accidentally develop water poisoning from daily drinking. The body's thirst mechanism is an effective regulator.

The first signs of water intoxication can be mild and include headache, nausea, vomiting, and bloating.

Infants under one year old should generally not be given plain water, as they get sufficient hydration from breast milk or formula. Because of their small body size, even a small amount of extra water can be dangerous.

If you or someone you know shows severe symptoms like confusion, seizures, or loss of consciousness after drinking excessive water, seek immediate emergency medical attention.

For endurance athletes who sweat heavily and only replenish with plain water, the risk is higher. The loss of sodium through sweat, combined with excessive water intake, can cause hyponatremia.

Hyponatremia causes brain cells to swell as water moves into them due to the low external sodium concentration. This increases pressure inside the skull and can lead to severe neurological symptoms and damage.

While most cases involve plain water, other fluids low in electrolytes can also contribute. Underlying medical conditions and certain drugs that affect the body's ability to excrete water can also be factors.