What Happens When You Drink a Ton of Water?

January 14, 2026 •

4 min read

According to Healthline, a healthy adult's kidneys can eliminate about one liter of water per hour. But what happens when you drink a ton of water and exceed this limit? Overconsumption can lead to a potentially fatal condition known as water intoxication or hyponatremia, where the body's sodium levels become dangerously diluted.

Quick Summary

Excessive water intake over a short period can overwhelm the kidneys, causing an electrolyte imbalance known as hyponatremia. This leads to cellular swelling and serious symptoms like headaches, confusion, and seizures.

Key Points

Hyponatremia is the core danger: Excessive water intake can dilute the body's sodium levels, leading to hyponatremia, a potentially fatal electrolyte imbalance.
Brain cells swell from overhydration: Low sodium levels cause water to rush into the cells, particularly the sensitive brain cells, leading to increased intracranial pressure and serious neurological symptoms.
Symptoms mimic other conditions: Mild water intoxication symptoms, such as headaches and nausea, can be mistaken for other issues, including dehydration.
Endurance athletes are a high-risk group: Those who perform prolonged, intense exercise and drink large quantities of plain water are especially susceptible to hyponatremia.
Listen to your thirst: The most reliable way for a healthy person to stay safely hydrated is to drink when thirsty and monitor urine color, which should be a pale yellow.
Kidney capacity is limited: A healthy adult's kidneys can only process about one liter of fluid per hour, so drinking significantly more than this in a short period is dangerous.

The Risks of Too Much Water

While proper hydration is vital for health, there is a dangerous tipping point where too much water can become a major problem. This condition, called overhydration or water intoxication, occurs when you drink more water than your kidneys can excrete, leading to an imbalance of electrolytes, particularly sodium. Your body functions best when there is a delicate balance of sodium and water, a balance that can be thrown into disarray by excessive fluid intake.

What is Hyponatremia?

Hyponatremia is the most critical consequence of drinking a ton of water too quickly. It is a condition defined by a dangerously low level of sodium in the blood (below 135 mEq/L). Sodium is an essential electrolyte that helps regulate the fluid balance inside and outside of your cells. When blood sodium levels plummet due to overhydration, water shifts from the bloodstream into the body's cells to balance the concentration. When this happens to brain cells, they swell, leading to increased pressure inside the skull, which can have life-threatening consequences.

Symptoms of Water Intoxication

The symptoms of water intoxication can range from mild to severe, and they often mimic signs of dehydration, making them easy to misinterpret.

Early symptoms include:

Nausea and vomiting
Persistent, throbbing headaches
Fatigue and drowsiness
Mental confusion or disorientation

Severe symptoms can include:

Muscle weakness, cramps, or spasms
Swelling (edema) in the hands, feet, and face
Double vision
Seizures
Coma or death in extreme cases

Who is at Risk?

While water intoxication is rare in the general population, certain groups are at a higher risk.

Endurance Athletes: Marathon runners, triathletes, and others who perform intense, prolonged exercise are at risk if they consume excessive plain water without replacing lost electrolytes (sodium).
Individuals with Certain Medical Conditions: People with congestive heart failure, kidney disease, or liver disease may have reduced kidney function, making them more susceptible to fluid imbalances.
Infants: A baby's small body weight and immature kidneys make them particularly vulnerable. Health experts advise against giving water to infants under six months of age.
Those with Mental Health Disorders: Conditions like schizophrenia can sometimes lead to psychogenic polydipsia, a compulsive water-drinking behavior.

The Effect on Your Kidneys and Brain

Your kidneys are the body's filtration system, responsible for maintaining a healthy fluid balance by removing waste and excess water from your blood. However, this capacity is limited. The kidneys of a healthy adult can process about one liter of water per hour. When you exceed this intake, you overwork your kidneys, and the excess water floods the body. This fluid accumulation dilutes the concentration of solutes, leading to cellular swelling throughout the body, with the brain being the most vulnerable organ. The brain is encased in the skull, and as its cells swell, the pressure increases. This is the underlying cause of many of the serious neurological symptoms associated with severe hyponatremia.

Hydration Comparison: Safe vs. Excessive


Factor	Safe Hydration	Excessive Hydration (Overhydration)
Fluid Intake	Drink based on thirst; spread intake throughout the day. Typical daily intake is 9-13 cups (including food) for average adults.	Compulsive or forced drinking of large volumes in a short period (e.g., more than 1 liter per hour).
Electrolyte Balance	Sodium levels remain stable, typically between 135 and 145 mEq/L.	Dangerous dilution of sodium in the blood (hyponatremia), with levels falling below 135 mEq/L.
Kidney Function	Kidneys efficiently excrete excess water, maintaining fluid balance.	Kidneys are overwhelmed, unable to excrete enough water, leading to fluid overload.
Urine Color	Pale yellow, like lemonade.	Clear or colorless.
Physical Symptoms	Healthy energy levels, no unexplained headaches or fatigue.	Headaches, nausea, fatigue, and potential muscle weakness or cramping.
Risk Level	Low risk of water intoxication in healthy individuals.	High risk, especially for athletes or those with underlying health issues.

Conclusion

While staying hydrated is crucial for overall health, it is a myth that more is always better. Drinking a ton of water can have serious, even fatal, consequences if the body's electrolyte balance is upset. The key to safe hydration is to listen to your body's signals, primarily thirst, and consume fluids steadily throughout the day rather than in large, rapid quantities. Monitoring urine color is another simple and effective indicator: aim for a pale yellow hue. If you are an athlete or have an underlying medical condition, paying attention to your body's cues and potentially using electrolyte-enhanced drinks is even more critical. Ultimately, moderation and mindfulness are the keys to a healthy hydration strategy. For more detailed information on water intoxication, consult the Cleveland Clinic website.

Frequently Asked Questions

Yes, although it's rare, drinking an extreme amount of water very quickly can lead to death due to severe hyponatremia and brain swelling.

Water intoxication is another name for overhydration, a condition where excessive fluid intake overwhelms the body's ability to regulate sodium and fluid balance, leading to a dangerous dilution of electrolytes.

There is no single amount that is 'too much' for everyone, as needs vary. However, drinking more than what your kidneys can filter—about 1 liter per hour for a healthy adult—can be risky.

Early signs often include headaches, nausea, vomiting, and fatigue. Monitoring urine color is also helpful, as colorless urine can indicate overhydration.

A good rule of thumb is to listen to your body's thirst signals. Additionally, your urine color should be a pale yellow; if it's clear, you may be overhydrated.

Yes, endurance athletes who sweat profusely and drink large volumes of plain water without replenishing electrolytes like sodium are at a higher risk.

If you or someone else is showing severe symptoms like confusion or seizures, seek immediate medical attention. In mild cases, stop drinking fluids and eat a salty snack.