What Does Drinking Sea Water Do to the Body? The Dangerous Truth

January 4, 2026 •

4 min read

Contrary to a misguided attempt to quench thirst, consuming seawater actually leads to more severe dehydration. This article explores what does drinking sea water do to the body, detailing the extreme risks and why it's a critical survival error. The high concentration of salt forces the body to expel precious fresh water, worsening your condition.

Quick Summary

Drinking seawater introduces toxic levels of salt into the body, forcing the kidneys to use vital bodily fluids to flush out excess sodium. This process creates a water deficit, leading to severe dehydration, organ damage, and potential death if fresh water isn't obtained.

Key Points

Severe Dehydration: Drinking seawater exacerbates dehydration because the high salt content forces the body to expel more water than it takes in to process the excess sodium.
Kidney Overload: Human kidneys are not designed to filter the high concentration of salt in seawater, requiring a large volume of the body's own fresh water to excrete it and causing extreme strain.
Electrolyte Imbalance: Excessive sodium intake from seawater disrupts the body's delicate electrolyte balance, leading to a dangerous condition called hypernatremia that affects nerve and muscle function.
Cellular Damage: The principle of osmosis causes water to be drawn out of body cells to dilute the bloodstream, leading to cellular shrinkage and dysfunction.
Organ Failure: Ingestion of seawater can cause nausea, vomiting, and severe dehydration, which, if not treated, can lead to widespread organ failure and death.
Survival Rule: For anyone stranded at sea, the core survival rule is to never drink seawater, as it only accelerates the process of dehydration and increases health risks.

The Immediate Physiological Response to Seawater

When a human drinks seawater, the body's delicate osmotic balance is thrown into chaos. Seawater contains an average salinity of 3.5%, significantly higher than the approximately 0.9% salt concentration of human blood. This hypertonic solution triggers a dangerous cascade of physiological events at the cellular level.

The Role of Osmosis and Cellular Dehydration

To function correctly, our cells rely on a balanced water-to-salt ratio. The principle of osmosis dictates that water will move from an area of lower salt concentration to an area of higher concentration to achieve equilibrium. When the bloodstream is flooded with the high salt content from seawater, the body's natural response is to draw water out of its own cells to dilute the saltier blood.

This process has several devastating effects:

Cellular Shrinkage: Water is pulled from cells, causing them to shrink and lose functionality.
Increased Thirst: The brain's thirst mechanism is triggered, yet drinking more seawater only exacerbates the problem, creating a vicious cycle.
Fluid Redistribution: Fluids are moved from vital tissues to the bloodstream, stressing the entire system.

Overburdening the Kidneys

The kidneys are the body's filters, regulating fluid and electrolyte balance. However, human kidneys are not equipped to handle the high salinity of seawater. They can only produce urine that is marginally less salty than the seawater ingested. To excrete the massive influx of salt, the kidneys must use more water than was consumed, resulting in a net loss of bodily fluids. For every liter of seawater ingested, the body needs approximately 1.6 liters of its own water to process it.

The Cascade of Health Consequences

The initial effects of cellular dehydration and kidney strain rapidly escalate into life-threatening conditions. The body's systems, from the digestive tract to the heart and brain, begin to fail under the toxic load.

Digestive Distress: The high salt content can irritate the stomach and intestines, leading to nausea, vomiting, and diarrhea. These symptoms cause further, rapid fluid loss, intensifying dehydration.
Hypernatremia and Electrolyte Imbalance: The excessive sodium in the blood, a condition known as hypernatremia, disrupts the balance of essential electrolytes like sodium and potassium. This can lead to irregular heart rhythms, muscle spasms, confusion, and neurological disturbances, with extreme cases resulting in seizures, coma, or death.
Organ Failure: As dehydration and hypernatremia worsen, the body diverts blood flow away from non-essential organs to preserve the brain and heart. This can lead to the shutdown of the kidneys and other vital organs.

Why Seawater is a Survival Hazard

For those stranded at sea, the temptation to drink seawater can be overwhelming. However, it is a fatal mistake. Survival experts and organizations like NOAA unequivocally state that drinking seawater is extremely dangerous. The body's systems simply cannot adapt to it.


Comparison of Seawater vs. Fresh Water Intake	Feature	Fresh Water (Potable)	Sea Water (Non-Potable)
Effect on Hydration	Replenishes bodily fluids; rehydrates.	Causes net fluid loss; dehydrates further.
Kidney Impact	Kidneys regulate fluid and excrete excess waste normally.	Kidneys are severely strained and use more water than consumed to excrete salt.
Salt Concentration	Low, within safe dietary levels.	High (approx. 3.5%), far beyond what human kidneys can process.
Electrolyte Balance	Maintains normal electrolyte levels.	Severely disrupts electrolyte balance, leading to hypernatremia.
Survival Outcome	Essential for survival.	Drastically decreases survival chances.

Conclusion

In summary, the human body is not designed to drink sea water. The high salt concentration triggers a counterintuitive and deadly chain reaction, starting with cellular dehydration and placing an unmanageable burden on the kidneys. The resulting hypernatremia and electrolyte imbalances can lead to a cascade of life-threatening health issues, from digestive distress to organ failure and death. For anyone in a survival situation, the critical lesson is to prioritize the collection of fresh, potable water and avoid the deadly temptation of the sea. For more information on the dangers of consuming seawater, you can reference resources from NOAA's National Ocean Service, which provides details on the physiological effects.

Note: This information is for educational purposes only and should not be used as medical advice. In any survival situation, prioritize seeking professional help and reliable sources of fresh water.

Potential Complications of Seawater Ingestion

Immediate Dehydration: Despite drinking, the body loses more water than it gains.
Gastrointestinal Distress: Nausea, vomiting, and diarrhea worsen fluid loss.
Electrolyte Imbalance: Critical minerals are thrown out of balance, affecting nerve and muscle function.
Kidney Failure: The organ system is overwhelmed by the salt load, leading to dysfunction or failure.
Neurological Symptoms: Confusion, delirium, and seizures can occur due to extreme hypernatremia.
Cardiovascular Strain: High blood pressure and an increased heart rate result from the body's efforts to compensate for fluid loss.

What happens to other creatures?

While humans cannot drink seawater, many marine animals possess specialized adaptations to do so. Seabirds have salt glands in their nostrils to excrete excess salt, and marine mammals like whales and seals have highly efficient kidneys.

Frequently Asked Questions

The primary reason is severe dehydration. Seawater contains a salt concentration so high that the kidneys must use more water from the body's reserves than was ingested to flush out the excess salt, leading to a net loss of fluids.

No, boiling seawater alone does not make it safe. While boiling kills potential microorganisms, it does not remove the salt. For seawater to be drinkable, the salt must be removed through a process called desalination, which typically requires specialized equipment not available in a survival scenario.

Marine animals like whales, seals, and seabirds have evolved special biological mechanisms to handle high salt intake. This includes highly efficient kidneys or specialized glands (like salt glands in seabirds) that can excrete excess salt.

Hypernatremia is a condition caused by dangerously high levels of sodium in the blood. Drinking seawater causes a massive influx of sodium, leading to hypernatremia which disrupts nerve and muscle function and can be fatal.

A person stranded at sea should never drink seawater. Instead, they should focus on conserving energy, seeking shelter from the sun, and attempting to collect rainwater. Survival experts advise against eating solid food without an adequate supply of fresh water.

The high salt concentration irritates the gastrointestinal tract. The body's attempt to reject the toxic substance leads to nausea and vomiting, which further depletes the body of vital fluids and accelerates dehydration.

No, accidentally swallowing a small amount of seawater while swimming is not typically harmful. The kidneys can handle minor salt intake, though it may cause a slight increase in thirst. The severe risks come from ingesting larger quantities as a substitute for fresh drinking water.