Boiling is a widely known method for purifying water from sources like lakes or rivers, leading many to wonder if it can also make seawater safe to drink. However, simply boiling seawater is not enough to render it potable. This common misconception overlooks the fundamental chemical differences between purifying freshwater and desalinating saltwater.
Why Boiling Alone Isn’t Enough
Boiling water effectively kills harmful microorganisms such as bacteria, viruses, and parasites by exposing them to high temperatures. This is sufficient to eliminate most waterborne pathogens, making contaminated freshwater sources safer for consumption by addressing biological threats.
Boiling, however, does not remove dissolved solids like salts, minerals, or heavy metals. When seawater boils, the water evaporates into steam, but the salt and other non-volatile impurities are left behind in the boiling vessel. As the pure water turns into steam, the remaining water in the pot becomes even saltier, concentrating the hazardous substances.
The boiling point of sodium chloride, the primary component of salt, is extremely high (around 1413 degrees Celsius). This means salt does not vaporize with the water. Therefore, boiling seawater in an open container only increases the concentration of salt in the remaining liquid, making it more dangerous to drink.
The Principles of Desalination
To make seawater drinkable, distillation is used. This process involves heating seawater to produce steam. The steam is then collected and cooled, causing it to condense back into liquid freshwater. The salts and other impurities remain in the original boiling chamber because they do not evaporate with the water.
This method mimics the natural water cycle, where evaporation purifies water, leaving behind contaminants. A basic distillation setup involves a heat source for the seawater, a mechanism to capture the rising steam, and a cooling surface to condense the steam into a separate container. The resulting condensed water is free from dissolved salts and many other impurities that boiling alone cannot remove.
Distillation differs from merely boiling water in an open pot because it collects the purified water vapor. This process separates the water molecules from the salt and other non-volatile compounds, yielding potable water. While effective, large-scale desalination plants often use more energy-efficient variations of distillation or other methods like reverse osmosis to produce freshwater at scale.
The Dangers of Drinking Seawater
Consuming untreated seawater poses severe health risks due to its high salt concentration. Seawater typically contains about 35 grams of salt per liter. Human kidneys are unable to produce urine with a salt concentration higher than approximately 2%. This means that to excrete the excess salt from seawater, the body must use more water than it has consumed.
When seawater is ingested, the high concentration of salt in the bloodstream creates a hypertonic environment, drawing water out of the body’s cells to dilute the blood. This process leads to severe dehydration as the body attempts to flush out the excess sodium. The kidneys are forced to work overtime, extracting water from the body’s reserves, which paradoxically increases dehydration rather than alleviating thirst.
Symptoms of drinking seawater include increased thirst, nausea, vomiting, diarrhea, and confusion. Continued consumption can lead to kidney failure and, eventually, death, as the body struggles to maintain its fluid and electrolyte balance. These dangers highlight why proper desalination methods are necessary for making seawater safe for human consumption.