Why We Don't Use Ocean Water to Drink

December 31, 2025 •

3 min read

While the ocean holds approximately 97% of the world's water, this vast resource is undrinkable for humans. The reasons go far beyond just the unpleasant salty taste, involving dangerous physiological reactions in the body and significant practical challenges that prevent us from using ocean water for drinking on a large scale.

Quick Summary

Drinking seawater is hazardous, causing severe dehydration and overtaxing the kidneys due to high salt content. Desalination, though possible, faces substantial economic and environmental challenges.

Key Points

Health Risks: Drinking ocean water is highly toxic, causing severe dehydration and salt poisoning that can lead to death due to the body's inability to process the high salt concentration.
Kidney Overload: The human kidneys are unable to excrete the excess salt from seawater, forcing them to use more water than is consumed, which worsens dehydration.
Energy Costs: Making ocean water drinkable through desalination requires massive amounts of energy and is an expensive process, making it unsustainable for widespread use.
Environmental Impact: Desalination plants can harm marine life through their water intake systems and the discharge of highly concentrated, heated brine.
Desalination Technology: Methods like Reverse Osmosis and thermal distillation exist, but are complex and costly, with Reverse Osmosis being the most common modern technique.
Limited Freshwater: Only about 3% of the world's water is freshwater, and a fraction of that is readily available for human use, despite the ocean's vast volume.

The Dangerous Health Effects of Drinking Ocean Water

The primary reason we don't use ocean water for drinking is its dangerously high salt content. Seawater typically contains about 3.5% dissolved salt, primarily sodium chloride. In contrast, the human body's blood has a much lower concentration. This difference is critical for a biological process called osmosis.

When a person ingests seawater, the high salt concentration in their bloodstream pulls water from their cells to dilute the sodium level. This process causes cells to shrink, leading to severe dehydration, even when consuming a fluid. Your thirst increases, but drinking more seawater only exacerbates the problem, creating a deadly cycle that can quickly lead to organ damage or death.

Your Kidneys Can’t Keep Up

Your kidneys are masterful filters, but they have a limit. They can produce urine that is less salty than your blood to remove excess sodium. However, the salinity of seawater is higher than the maximum salt concentration your kidneys can excrete. To get rid of the excessive salt load from drinking ocean water, your kidneys would need to use more water than you ingested, resulting in a net fluid loss. For individuals with pre-existing conditions like hypertension or kidney disease, the risks are even higher.

Contaminants and Pollutants

Besides salt, the ocean contains other harmful substances. Seawater can be contaminated with bacteria, viruses, and parasites from animal waste and runoff. Boiling the water kills microorganisms but does not remove the salt, making it unsafe to drink. Marine pollution also adds industrial toxins, chemical waste, and microplastics to the water, posing additional health risks if ingested.

Desalination: A Costly and Energy-Intensive Process

While science has developed methods to make ocean water drinkable through desalination, this process is not without significant hurdles. Large-scale desalination plants require immense amounts of energy, making them expensive to operate and environmentally impactful. There are two main methods used:

Reverse Osmosis (RO): This is the most widely used desalination method, involving high pressure to force seawater through semipermeable membranes. These membranes filter out salt and other minerals, leaving freshwater behind. The technology has become more efficient but remains energy-intensive.
Thermal Distillation: This older technique involves boiling seawater and collecting the steam as it condenses back into pure water. It is even more energy-intensive than reverse osmosis but can be effective when paired with power plants that produce waste heat.

Environmental and Economic Drawbacks

The environmental costs associated with desalination are a major concern. The intake of seawater can harm marine life by drawing in small organisms like plankton and fish larvae. Additionally, the process produces a highly concentrated brine byproduct, which is often discharged back into the ocean. This discharge can increase the salinity and temperature of the surrounding marine environment, harming ecosystems unless carefully managed.

Economically, the high energy demands make desalination prohibitively expensive for many water-stressed nations, especially in comparison to traditional freshwater sources. While costs have decreased over the years, the financial investment in large-scale plants and ongoing energy expenses remain a barrier for many regions.

Comparison: Ocean Water vs. Tap Water


Characteristic	Ocean Water	Tap Water (Freshwater)
Salinity	Average 3.5% (35 ppt)	Very low (<0.1%)
Sodium Content	~10,752 mg/L	Regulated to minimal levels
Toxicity	Highly toxic to humans	Safe for human consumption
Taste	Extremely salty	Neutral/Mineral taste
Processing	Requires complex, energy-intensive desalination	Filtered and disinfected at lower cost
Environmental Impact	Significant energy use and brine pollution from processing	Less intensive processing, potentially local source concerns
Immediate Effect	Causes rapid dehydration	Rehydrates the body effectively

Conclusion

In conclusion, the decision to not use ocean water for drinking is a matter of basic human physiology and resource management. The dangerously high salt content overwhelms our kidneys and leads to severe dehydration and potential death. While technologies like desalination can remove the salt, the process is expensive, requires immense energy, and carries significant environmental consequences. These factors make it impractical and unsustainable for widespread adoption, particularly when compared to managing and protecting our existing, precious freshwater supplies. For these reasons, the best source of drinking water remains fresh, purified sources found on land. For more information on this and other topics, please visit the NOAA National Ocean Service.

Frequently Asked Questions

Accidentally swallowing a small amount of ocean water, like while swimming, is unlikely to cause serious harm, especially if you are properly hydrated. Your body can process very small amounts of salt without significant issue.

No, boiling ocean water does not make it safe to drink. While boiling will kill microorganisms and parasites, it does not remove the salt. The concentration of salt would actually increase as the freshwater evaporates, making it even more dangerous to consume.

Certain marine animals, like seabirds and some mammals, have highly specialized organs or kidneys that allow them to process and excrete the large amount of salt they ingest. Humans do not have this physiological adaptation.

While desalination is a viable option for some arid coastal regions and a growing industry, it faces major challenges. High energy costs and significant environmental impacts from brine discharge mean it is not a simple or universal solution for global water shortages.

In simple terms, reverse osmosis is a process where pressure is used to push saltwater through a very fine filter (a semipermeable membrane). The water molecules can pass through, but the larger salt molecules are left behind, resulting in purified freshwater.

In a survival situation, the safest way to get freshwater from the ocean is through distillation. This can be done with a basic solar still, which uses the sun's heat to evaporate and condense water vapor, leaving the salt behind.

Consuming seawater can also lead to electrolyte imbalances, which affect heart, nerve, and muscle function. In addition, it can cause nausea, vomiting, and diarrhea, further intensifying dehydration and putting additional strain on the body.