What happens if you drink 20 bottles of water? The Dangers of Overhydration

December 11, 2025 •

3 min read

Your kidneys can only process about one liter of water per hour. Chugging twenty 16.9-ounce (approx. 0.5 liter) bottles of water in a short period would massively exceed this capacity, leading to a dangerous and potentially fatal medical emergency known as water intoxication.

Quick Summary

Consuming 20 bottles of water too quickly can cause water intoxication (hyponatremia), diluting blood sodium levels, causing brain swelling, and leading to severe health complications like seizures or coma.

Key Points

Hyponatremia Risk: Drinking a large volume of water quickly can cause a dangerous drop in blood sodium levels, leading to hyponatremia.
Kidney Overload: The kidneys can only process about one liter of water per hour, and excessive intake overwhelms their ability to excrete fluid.
Brain Swelling: Low sodium levels cause water to move into cells, including brain cells, resulting in dangerous brain swelling (cerebral edema).
Severe Symptoms: Water intoxication can cause severe neurological symptoms like confusion, seizures, coma, and can even be fatal.
Listen to Your Body: The best way to prevent overhydration is to drink when you are thirsty and monitor your urine color, which should be pale yellow.
Emergency Treatment: Severe cases are a medical emergency and may require IV saline and diuretics to correct the electrolyte imbalance.

The Risk of Water Intoxication

While we are often reminded of the importance of staying hydrated, excessive water intake over a short period can be lethal. This condition, known as water intoxication or dilutional hyponatremia, is caused by the dilution of the body's sodium levels. A typical 16.9-ounce bottle of water holds approximately 0.5 liters. Drinking 20 of these bottles amounts to 10 liters, a quantity far exceeding the kidneys' capacity to excrete water in a short time frame. This creates a severe electrolyte imbalance that can disrupt the functioning of the entire body, especially the brain.

The Physiological Cascade of Excessive Water Intake

When you consume a large amount of water rapidly, your body's sodium levels become critically diluted. Sodium is a vital electrolyte that helps regulate the balance of fluids both inside and outside of your cells. As the blood's sodium concentration plummets below 135 mEq/L, a state of hyponatremia occurs. To balance the concentration difference, water from the bloodstream moves into the body's cells, causing them to swell. This is particularly dangerous for brain cells, which are contained within the rigid confines of the skull. The resulting brain swelling, or cerebral edema, increases pressure on the brain, leading to severe and life-threatening symptoms.

Symptoms of Water Intoxication

The symptoms of water intoxication vary depending on the severity of the hyponatremia. In the initial stages, they can be subtle and easily confused with dehydration.

Mild to Moderate Symptoms:

Nausea and vomiting
Headache
Confusion or disorientation
Drowsiness and fatigue
Muscle weakness, cramps, or spasms
Bloating or swelling in the hands, feet, or face

Severe Symptoms:

Increased blood pressure
Double vision
Difficulty breathing
Seizures
Coma
Death

Real-World Consequences: A Tragic Example

The dangers of water intoxication are well-documented, often tragically highlighted by water-drinking competitions. A prominent case involved a radio contest in 2007, where a woman died after consuming nearly two gallons (almost 8 liters) of water in a short period. Other cases have occurred in endurance athletes who mistakenly over-hydrate during strenuous events.

Comparison: Water Intoxication vs. Dehydration

While seemingly opposite conditions, water intoxication and dehydration can present with similar initial symptoms, making self-diagnosis difficult. Key differences, however, highlight the urgency and unique risks of overhydration.


Feature	Water Intoxication (Overhydration)	Dehydration
Underlying Cause	Excess water dilutes blood sodium (hyponatremia).	Insufficient water leads to low blood volume and high sodium concentration.
Urine Color	Clear or colorless.	Dark yellow, potentially with a strong odor.
Thirst Level	May not be thirsty; potentially excessive drinking due to psychological factors or medication.	Typically accompanied by intense thirst.
Cellular Effect	Cells swell as water moves into them.	Cells shrink as water moves out of them.
Primary Threat	Brain swelling (cerebral edema), seizures, coma.	Hypovolemic shock, heatstroke, organ damage.
Risk Factors	Endurance athletes, certain medications, kidney/liver issues, mental health conditions.	Illness with vomiting/diarrhea, strenuous activity in heat, older age.

The Emergency Response to Water Intoxication

If you suspect someone is suffering from water intoxication, particularly if severe symptoms like confusion or seizures are present, immediate medical attention is critical. Mild cases can sometimes resolve by restricting fluid intake and allowing the body to rebalance naturally. However, severe cases require urgent treatment to prevent permanent brain damage or death.

Medical interventions may include:

Fluid Restriction: Immediately stop consuming fluids.
Electrolyte Replacement: Administering a hypertonic saline solution intravenously (IV) to gradually increase blood sodium levels.
Diuretics: Medications like diuretics can help increase urine output to flush excess water from the body.
Addressing Underlying Causes: Treatment for any underlying medical conditions or psychological issues, if present, that contributed to the excessive fluid intake.

For more information on water intoxication, you can visit the Cleveland Clinic website.

Conclusion

While the concept of drinking 20 bottles of water may seem extreme, the lethal potential of overhydration is a serious medical reality. It is crucial to listen to your body's thirst signals and maintain a balanced approach to fluid intake rather than forcing consumption beyond your needs. The severe consequences of hyponatremia, from brain swelling to fatality, underscore the importance of recognizing the signs of water intoxication and seeking immediate medical help when needed. A healthy hydration strategy involves moderation and paying attention to your body's natural cues, not blindly following rigid, excessive water intake goals.

Frequently Asked Questions

Water intoxication is a medical emergency caused by drinking excessive amounts of water in a short period. This dilutes the body's sodium concentration, leading to a condition called hyponatremia, which causes cells to swell.

Water intoxication can occur within hours if a very large volume of water is consumed. Symptoms often appear after drinking more than a liter or so per hour, depending on individual factors like body size and kidney function.

Early symptoms often include headaches, nausea, vomiting, fatigue, and muscle weakness. These can be easily confused with dehydration, but the key is excessive recent water intake.

Yes, in severe cases, the brain swelling caused by water intoxication can lead to seizures, coma, and death. Fatal incidents have been documented in water-drinking contests and among athletes.

Severe water intoxication requires immediate medical treatment, which typically involves restricting fluid intake, administering intravenous hypertonic saline to correct sodium levels, and possibly diuretics to increase urine output.

A key indicator is urine color: clear or colorless urine suggests overhydration, while dark yellow urine indicates dehydration. Your level of thirst is also a good guide.

Endurance athletes who drink excessive water during long events are at high risk. Other groups include individuals with certain kidney or liver conditions, those on specific medications, and people with psychological disorders involving compulsive water drinking.