Seawater's dangers are well-known thanks to the line from Samuel Taylor Coleridge that states, "Water, water, everywhere, nor any drop to drink." While the line from "The Rime of the Ancient Mariner" warns that the ocean's water is not fit for drinking as the ship's occupants are stranded at sea, it does not explain why seawater is taboo or exactly how it causes dehydration.
Saline Content
Seawater contains an extremely high amount of salt, with about 35,000 parts per million, or ppm, according to the U.S. Geological Survey. Comparatively, fresh water that is safe for drinking contains less than 1 ppm of saline. Although ocean water has the highest saline level of any naturally occurring water on Earth, saline water from other sources can also be detrimental. Slightly saline water contains 1,000 to 3,000 ppm of salt, moderately saline water contains 3,000 to 10,000 ppm and highly saline water contains 10,000 to 35,000.
Body Reaction
Seawater causes dehydration due to your body's reaction to such a high level of saline, according to the American Museum of Natural History and Lenntech websites. When the saline enters your body, the saline begins to absorb you body's water through osmosis, robbing your cells of the water they need to function. Your body's automatic reaction is to dilute the saline and flush it out of your system. If you drink seawater, the amount of water your body needs to dilute and flush out the saline is higher than the amount of water you drink. You become thirsty due to the lack of water in your body's cells. Death from kidney failure can also result as the kidneys can no longer eliminate waste and extra fluids from your blood, according to MayoClinic.com.
Other Symptoms
Dehydration from drinking seawater can range from mild to extreme, depending on the amount of seawater consumed. Mild symptoms include mild thirst, dizziness, dry skin, constipation, decreased urination, headache and fatigue. In addition to kidney failure, other severe symptoms include severe thirst, confusion, lack of tears, urination and sweat, shriveled skin and sunken eyes, low blood pressure, rapid heartbeat and breathing, fever, unconsciousness and death.
Considerations
Severe signs of dehydration merit immediate medical attention, according to the Mayo Clinic website. Complications from dehydration include swelling of the brain, seizures and hypovolemic shock, which occurs when your blood volume drops low enough to reduce your blood pressure as well as the oxygen levels in your body. Animals that live in and around seawater have adapted to their environment, the American Museum of Natural History reports. Saltwater fish, for example, have specialized cells in their gills that, along with their kidneys, help flush out large levels of salt.
