What does drinking salt water do to your body?

October 31, 2025 •

3 min read

Seawater is approximately 3.5% salt, a concentration far higher than the human body can safely process. What does drinking salt water do to your body? The consequences can be severe, including rapid dehydration, kidney damage, and electrolyte imbalances that can be life-threatening.

Quick Summary

Consuming water with a high salt concentration disrupts the body's delicate fluid balance, leading to cellular dehydration and placing immense strain on the kidneys. Severe health risks, including hypernatremia and organ damage, are major concerns and it is not a safe source of hydration.

Key Points

Causes Dehydration: Drinking saltwater forces your body to use its own water reserves to flush out the excess salt, leading to a net loss of fluid and worsening dehydration.
Strains the Kidneys: Your kidneys can't produce urine as salty as seawater, so they must use more water to process and excrete the salt, putting them under severe stress.
Induces Hypernatremia: Excessive sodium intake from saltwater consumption leads to an dangerously high concentration of sodium in the blood, disrupting nerve and muscle function.
Increases Thirst: The high salt content makes you feel even thirstier, creating a deceptive and dangerous cycle of drinking more saltwater and accelerating dehydration.
Can be Fatal: In severe cases, drinking saltwater can lead to organ failure, neurological issues, coma, and death due to the extreme physiological stress.
Worse Than No Water: In a survival situation, drinking seawater is more harmful than abstaining from water entirely because it speeds up the dehydration process.

The Science of Dehydration: How Osmosis Works

At its core, the danger of drinking salt water is a matter of physiology and basic science. Your body's cells are surrounded by a semi-permeable membrane that regulates the flow of water and other substances. When you drink water with a salt concentration higher than that of your blood, a process called osmosis occurs. The high salt content in your bloodstream creates a hypertonic environment, causing water to be drawn out of your body's cells to dilute the salt. This cellular dehydration is the exact opposite of what your body needs for hydration, and it is the primary reason why drinking salt water is so harmful.

The Kidney's Overload: A Failed Filtering Process

Your kidneys are responsible for filtering out waste and regulating the balance of fluids and electrolytes, including sodium, in your body. When faced with the high sodium load from salt water, your kidneys go into overdrive to excrete the excess salt. However, the kidneys can only produce urine that is less salty than seawater. This means that to flush out the high concentration of salt you ingested, your kidneys must use more water than you actually drank. This creates a vicious, counterproductive cycle: you drink to hydrate, but your body uses even more water to expel the salt, leading to a net loss of fluid and worsening dehydration. Over time, this intense strain can cause kidney damage or even complete failure.

Severe Symptoms and Risks of Salt Water Ingestion

Drinking too much salt water can quickly lead to a range of severe symptoms, and in large quantities, it can be fatal. The resulting condition of having abnormally high sodium levels in the blood is known as hypernatremia.

Common symptoms include:

Extreme Thirst: The body's immediate response to the high sodium concentration.
Nausea and Vomiting: The body's attempt to expel the excess salt, further contributing to fluid loss.
Diarrhea: The body attempts to flush out the irritant, compounding the dehydration.
Neurological Distress: Confusion, delirium, hallucinations, muscle twitching, and eventually seizures can result from the electrolyte imbalance and cellular changes in the brain.
Increased Heart Rate and Blood Pressure: The cardiovascular system constricts blood vessels to compensate for fluid loss.
Organ Failure: As dehydration and electrolyte imbalances worsen, major organs like the kidneys and brain can fail, leading to coma and death.

Survival Situation: Why Seawater is Worse Than Nothing

For a person in a survival situation, such as being stranded at sea, the decision to drink seawater is often a desperate one, but it is the wrong choice. In a famous summary of 163 life raft voyages, the risk of death was 39% for those who drank seawater, compared to only 3% for those who did not. Drinking nothing at all is a better option because it allows the body to conserve existing fluids, while drinking salt water actively accelerates the body's dehydration and hastens death. Survivors should focus on finding fresh water sources like rainwater or using desalination methods.

Comparison: Salt Water vs. Fresh Water Hydration


Feature	Fresh Water	Salt Water (e.g., Seawater)
Effect on Kidneys	Processed easily; kidneys excrete excess fluid naturally to maintain balance.	Causes immense strain; kidneys must use more water than ingested to expel salt, leading to dehydration.
Cellular Impact	Rehydrates cells, allowing for normal function and nutrient transport.	Draws water out of cells via osmosis, causing cellular dehydration and shrinkage.
Thirst Level	Quenches thirst and provides essential hydration.	Increases thirst dramatically, as the body signals the need for more water to dilute the salt.
Electrolyte Balance	Essential for maintaining healthy electrolyte balance in appropriate doses.	Severely disrupts electrolyte balance, causing dangerous levels of sodium (hypernatremia).
Overall Health	Critical for survival and maintaining optimal bodily functions.	Potentially fatal, leading to organ damage, seizures, and death.

Conclusion: The Dangers are Clear

What does drinking salt water do to your body? It initiates a destructive process of dehydration and cellular distress that places tremendous strain on vital organs. The osmotic effects cause water to be pulled from your cells, while your kidneys struggle and ultimately fail to process the overwhelming amount of salt. Far from providing hydration, drinking saltwater exacerbates dehydration, leading to a cascade of dangerous symptoms and, potentially, death. Relying on fresh, potable water is not just the best choice—it is the only safe and sustainable one. For more information on the dangers of consuming seawater, you can reference the resources available from the NOAA National Ocean Service.

Frequently Asked Questions

Our kidneys have a limited ability to concentrate urine. The salt content of seawater (approx. 3.5%) is much higher than what our kidneys can efficiently filter. To excrete the salt, our kidneys must use more water than we consumed, leading to a net loss of fluid.

No. While proponents of 'salt-water flushes' claim benefits, there is no scientific evidence to support this, and even small amounts increase your daily sodium intake and can cause mild dehydration. For most people, a diet already includes more than enough sodium.

Swallowing a small amount of seawater, such as while swimming, is not harmful. Your body can process this minimal amount without major issues. The danger lies in consuming it intentionally in large quantities.

No. Medical saline solutions have a precise salt concentration of about 0.9%, which is isotonic, or balanced with the salt levels in our blood. This allows for hydration without disrupting the body's osmotic balance, unlike highly concentrated seawater.

Some marine animals have evolved specialized organs, such as highly efficient kidneys in marine mammals or special salt glands in seabirds, that allow them to effectively filter and excrete the excess salt from seawater.

Boiling seawater will kill bacteria and other microorganisms, but it will not remove the salt. The salt will remain, and the resulting water will still be unsafe to drink. Distillation is required to separate the salt from the water.

Never drink seawater. The best course of action is to conserve energy and fluids, seek shade, and prioritize finding alternative fresh water sources like rainwater. Drinking seawater will only worsen your condition and speed up the dehydration process.