What is it called when you drink too much sea water?

January 7, 2026 •

4 min read

According to the National Ocean Service, the average salinity of seawater is about 3.5%, a concentration far too high for human kidneys to process effectively. When a person drinks too much seawater, the resulting medical condition is officially called hypernatremia, or high sodium levels in the blood, which can lead to a dangerous form of salt poisoning.

Quick Summary

Excessive consumption of seawater causes hypernatremia, or salt poisoning, due to the high sodium content. This forces the kidneys to work harder, leading to severe cellular dehydration, electrolyte imbalances, and potential organ damage.

Key Points

Hypernatremia: The medical term for the excessive intake of sea water is hypernatremia, or dangerously high sodium levels in the blood.
Salt Poisoning: Consuming large quantities of sea water leads to a toxic condition known as salt poisoning, with potentially fatal results.
Cellular Dehydration: Due to osmosis, the high salt content in the bloodstream pulls water out of the body's cells, causing them to shrink and worsening dehydration.
Kidney Overload: The kidneys, which cannot produce urine saltier than sea water, are overwhelmed and require more water to flush out the excess salt than you consumed.
Neurological Issues: The resulting electrolyte imbalance can disrupt nerve function, causing confusion, muscle twitching, and, in severe cases, seizures and coma.
Survival Rule: It is better to drink no water at all than to drink sea water in a survival situation, as it will hasten dehydration and death.
Distillation: The only safe way to drink sea water is by removing the salt through distillation, a process that can be done with a solar still or by boiling.

Hypernatremia: The Medical Term for Salt Overload

When you drink a large quantity of sea water, the medical term for the resulting high concentration of sodium in the blood is hypernatremia. The body’s cells, which rely on a delicate balance of water and electrolytes, are severely impacted by this rapid influx of salt. This condition is an instance of salt poisoning, a life-threatening situation where the body's sodium levels become toxic.

The Osmotic Effect: Why Salt Water Dehydrates You

The reason drinking salt water makes you more dehydrated is due to a biological process called osmosis. Your body's cells are surrounded by a semi-permeable membrane that regulates the flow of water. When the salt concentration in your blood becomes higher than the concentration inside your cells, water is drawn out of the cells to dilute the salt in the bloodstream. This process, driven by the body's attempt to restore balance, effectively shrinks your cells and makes you more dehydrated. Instead of quenching your thirst, consuming seawater actually compounds the problem, forcing your body to use its own water reserves to try and flush out the excess salt.

How Your Kidneys Respond to Excessive Salt

Your kidneys are the body's primary filtration system and are responsible for managing salt and water balance. However, human kidneys have a limitation: they cannot produce urine that is saltier than seawater. To excrete the high sodium concentration from the ocean, they need to use a significant amount of fresh water from your body. This creates a vicious and dangerous cycle: the more seawater you drink, the more fluid your kidneys must expend to eliminate the salt, leading to an ever-increasing state of dehydration. This places immense stress on the kidneys and can eventually cause renal failure.

Health Consequences of Drinking Seawater

The effects of consuming too much sea water range from mild to life-threatening. The high levels of sodium disrupt the body's intricate systems, triggering a domino effect of dangerous symptoms.

Increased Thirst: Paradoxically, drinking salt water will make you feel even thirstier as your body signals its need for fresh water to flush out the excess sodium.
Nausea and Vomiting: The body's natural defense mechanism will often trigger nausea and vomiting in an attempt to expel the toxins. This only worsens dehydration by further depleting fluids.
Neurological Symptoms: As sodium levels rise, it can interfere with nerve function. This may lead to confusion, disorientation, muscle twitching, and even seizures.
Organ Damage: The stress placed on the kidneys, heart, and brain can lead to serious organ damage. In extreme cases, the swelling of brain cells against the skull can lead to coma and death.
Digestive Distress: Beyond nausea, the high salt content can cause gastrointestinal issues, including severe diarrhea and abdominal pain, further accelerating fluid loss.

Why Salt Poisoning from Seawater is Different

While consuming small amounts of extra salt in food is common, the concentration in sea water is far beyond what the human body can handle. For instance, medical-grade saline solution contains a much lower, isotonic salt concentration (0.9%) that does not disrupt the body's osmotic balance. Seawater, at about 3.5% salinity, creates a hypertonic environment that actively pulls water from your cells. This is a critical distinction in understanding why sea water is so dangerous to drink for hydration.

Comparison: Drinking Sea Water vs. Fresh Water


Feature	Drinking Too Much Sea Water	Drinking Too Much Fresh Water (Overhydration)
Effect on Hydration	Leads to severe dehydration (hypernatremia) due to excess salt.	Can lead to water toxicity (hyponatremia) by diluting blood sodium levels.
Salt Concentration	Excessively high (approx. 3.5%).	None, leading to extremely low blood sodium levels.
Kidney Impact	Places massive stress on kidneys, potentially causing renal failure.	Kidneys struggle to excrete the massive influx of pure water.
Cellular Response	Water is pulled out of cells (osmosis).	Water moves into cells, causing them to swell (osmosis).
Initial Symptoms	Increased thirst, nausea, restlessness.	Nausea, vomiting, headache.
Severe Symptoms	Delirium, seizures, organ failure, coma.	Seizures, coma, potentially death.

Survival Alternatives to Drinking Sea Water

In a survival scenario, drinking sea water is a last resort that will accelerate dehydration and death. Survivors should prioritize finding fresh water through alternative methods:

Solar Still: A low-tech distillation method using the sun to evaporate sea water and condense the pure vapor into a collection cup.
Rainwater Collection: Gathering rain is the simplest and safest way to obtain fresh drinking water.
Beach Well: Digging a well past the high tide line can sometimes yield a layer of fresh water floating atop the denser saltwater.
Modern Desalinators: Emergency life rafts often include hand-pump reverse osmosis filters or solar stills, which are highly effective.

Conclusion: The Peril of Excessive Sea Water Consumption

Consuming too much sea water triggers a dangerous medical condition known as hypernatremia, a severe form of salt poisoning. Instead of providing hydration, the high concentration of salt forces the body to use its precious fresh water reserves to flush out the excess sodium. This process leads to rapidly worsening dehydration, electrolyte imbalances, and potentially fatal damage to vital organs such as the kidneys and brain. In any survival situation, it is critical to avoid drinking sea water and instead focus on collecting or distilling fresh water through alternative means. While a small, accidental gulp is not likely to be lethal, relying on sea water for hydration is a decision that will hasten your demise.

How to create a solar still for fresh water in an emergency:(https://www.wikihow.com/Desalinate-Water)

Frequently Asked Questions

Humans cannot drink sea water because its salt concentration is too high for our kidneys to process efficiently. To eliminate the excess salt, the body must use more water than it gains from drinking it, leading to a net loss of fluid and severe dehydration.

Accidentally swallowing a small amount of sea water is not harmful, especially if you are properly hydrated with fresh water. The danger arises from drinking it intentionally for hydration, as the cumulative effect of the high salt content is what causes the body to fail.

Immediate symptoms include increased thirst, nausea, and vomiting as the body attempts to expel the high salt concentration. This reaction is followed by restlessness and fatigue as dehydration takes hold.

The primary cause of death is severe dehydration leading to multiple organ failure. High blood sodium levels cause cells to lose water, which can trigger seizures, cardiac arrhythmia, and, ultimately, death.

Marine mammals and birds, unlike humans, have evolved special biological mechanisms to handle high salt intake. For example, some seabirds have salt glands that excrete excess salt, and whales have highly efficient kidneys.

The best methods for survival at sea include collecting rainwater, which is naturally distilled, or using a makeshift solar still to purify seawater through evaporation and condensation.

Hypernatremia is a condition of dangerously high sodium levels in the blood, often caused by severe dehydration or consuming sea water. Hyponatremia, in contrast, is the condition of dangerously low sodium levels, which can be caused by overhydration with pure water.