Despite the vastness of the world’s oceans, humans cannot safely consume seawater. Although water is fundamental for survival, the high salt content of ocean water makes it toxic to the human body. Our biological systems are simply not equipped to process such high concentrations of dissolved minerals, leading to consequences that actively work against hydration.
High Salt Content
Seawater contains a significant amount of dissolved salts, known as salinity. On average, ocean water has a salinity of about 3.5%, meaning each liter contains about 35 grams of dissolved salts. The primary salt found in seawater is sodium chloride, the same compound as common table salt.
This concentration is considerably higher than the salt levels found within the human body. For instance, human blood plasma maintains a salt concentration of around 0.9%. Our physiological systems operate within a narrow range of salt balance, and exceeding this limit poses a serious challenge.
Cellular Dehydration and Osmosis
Consuming seawater introduces excessive salt into the bloodstream, creating an imbalance with the fluid inside body cells. To correct this, osmosis occurs.
Osmosis is the movement of water molecules across a semi-permeable membrane, like a cell wall, from an area of higher water concentration (lower solute) to lower water concentration (higher solute). As blood becomes saltier from drinking seawater, water is drawn out of the body’s cells into the bloodstream. This cellular dehydration causes cells to shrink, impairing their normal functions and potentially leading to their demise.
The Kidneys’ Struggle
The kidneys play a central role in maintaining the body’s fluid and electrolyte balance, continuously filtering blood to remove waste and regulate water and salt levels. However, they require water to excrete excess salt.
When faced with seawater’s high salt load, kidneys must work overtime to remove it. The maximum salt concentration human kidneys can produce in urine is roughly 2.1%. Since seawater is 3.5% salt, excreting the salt from just one liter of seawater requires more than one liter of water. This leads to a net water loss, intensifying dehydration rather than alleviating it.
The Dehydration Spiral
The physiological responses to drinking seawater create a dangerous cycle. Instead of hydrating, consuming salty ocean water causes a greater water loss than ingested. This rapidly accelerates dehydration, making the situation worse than if no water had been consumed.
Symptoms of severe dehydration quickly manifest, including intense thirst, dizziness, nausea, and vomiting. As dehydration progresses, individuals may experience reduced urine output, muscle cramps, confusion, and delirium. Ultimately, the body’s continued struggle to excrete excess salt without sufficient water can lead to organ failure, shock, and death.