By Chris Deziel | Updated Mar 24, 2022
While the myth that humans are made of seawater persists, the reality is nuanced. The average adult body contains roughly 60 % water—slightly less saline than ocean water. The modest difference in salinity is what determines whether drinking salt water will hydrate or dehydrate you. When you ingest seawater, the sodium and chloride ions raise blood osmolality, prompting water to leave the cells. The resulting cellular shrinkage and eventual cell death can lead to fatal dehydration.
Osmosis can be observed with a simple kitchen experiment: dissolve ½ cup of table salt in a quart of water and submerge a carrot. After a day or two, the carrot will shrivel, mirroring what happens to bodily cells after consuming salt water. The semi‑permeable cell membrane allows water to pass but blocks ions. As salt concentration in the bloodstream rises, osmotic pressure increases, driving water out of the cells. Although your body may hold extra water, you feel thirstier than before.
Frequent consumption of salty water overwhelms the kidneys. During filtration, water moves across a semi‑permeable membrane into the kidney’s collecting ducts. If the blood’s salt concentration is too high, water cannot cross, reducing filtration efficiency. This creates a backlog of solutes, elevating blood pressure and imposing additional stress on the kidneys, heart, and liver. Chronic exposure can lead to kidney dysfunction or failure.
Body fluids contain sodium chloride, but the concentration in tears is about one‑third that of seawater. Excess sodium is expelled through urine, but repeated high intake can provoke cardiovascular disease. The body naturally cycles sodium and water over weeks or months, so occasional consumption is less harmful than regular ingestion. When you feel thirsty, drink plain water to dilute blood sodium and protect organs. Athletes may use salt tablets to replenish electrolytes lost in sweat, but they should be taken under professional guidance.
