Ocean water averages 3.5% salinity, significantly higher than the 0.9% salt concentration in human blood. Consuming this water introduces an excess of sodium and chloride ions, immediately disrupting the body’s fluid management systems. The primary danger is the acceleration of severe dehydration and systemic toxicity.
How the Body Reacts to High Salt Intake
The core problem with consuming seawater is its hypertonicity—it contains a much higher concentration of solutes than the body’s cells. This initiates osmosis, a destructive process where water moves across semipermeable cell membranes.
When seawater enters the digestive system, the high salt content is absorbed into the bloodstream, making the blood and extracellular fluids hypertonic. To correct this imbalance, water is drawn out of the body’s cells, causing them to shrink and compromising normal cell function.
The kidneys attempt to filter and excrete this sudden, massive influx of salt to restore electrolyte balance. However, the maximum concentration of salt the human kidney can produce in urine is significantly less than the salt concentration found in ocean water. This physiological limitation means that to excrete the excess sodium and chloride ions, the kidneys must use more fresh water from the body’s reserves than the amount of seawater originally consumed.
For every liter of ocean water consumed, the body requires approximately one and two-thirds liters of fresh water to flush the excess salt. This results in a net loss of hydration, rapidly accelerating the dehydration the person was attempting to relieve. Acute symptoms include muscle cramps, weakness, and intense thirst. The body may also attempt to expel toxins through nausea, vomiting, and diarrhea, which further accelerates fluid loss.
Additional Risks from Biological and Chemical Contaminants
Beyond the immediate threat of salt toxicity, ocean water contains contaminants that pose secondary health risks. Coastal areas are susceptible to biological threats, including pathogens from sewage and agricultural runoff. These hazards include bacteria, such as the Vibrio species, which can cause severe infections.
Ocean water frequently contains viruses and parasites introduced from untreated wastewater. Ingestion of these microorganisms can lead to gastrointestinal illnesses, such as severe stomach cramps and persistent diarrhea, which compound the dehydration caused by the high salt content.
Chemical pollution represents another danger, often originating from land-based activities. This includes industrial discharges containing heavy metals like mercury, agricultural pesticides, and petroleum-based pollutants. Harmful algal blooms, or “red tides,” release potent natural toxins. Contaminants like polychlorinated biphenyls (PCBs) and microplastics persist in the marine environment and introduce systemic toxins upon ingestion.
What to Do After Accidental Ingestion
If only a small amount of ocean water is accidentally swallowed, the body can usually process the salt without serious effects. The individual should immediately begin drinking fresh, unsalted water to help dilute the ingested salt. Avoid consuming diuretic substances like caffeine or alcohol, as these increase urine output and exacerbate fluid loss.
If a large quantity of seawater was consumed, such as in a maritime survival situation, the priority is to seek medical attention as soon as possible. Severe vomiting, persistent diarrhea, or confusion are signs of significant dehydration and electrolyte imbalance that require professional intervention. In such cases, the medical team can administer intravenous fluids to correct the hypertonic state more effectively than oral rehydration alone. Calling a poison control center can also provide immediate, specific recommendations tailored to the amount and source of the water ingested.