Boiling saltwater does not make it drinkable; instead, it makes the remaining water more concentrated and dangerous for human consumption. While boiling is a necessary first step in purifying water, it fails to remove the dissolved salts that make the water harmful. Attempting to quench thirst with boiled saltwater can lead to severe physiological consequences.
Boiling Only Kills Pathogens
Boiling is an effective method for microbiological purification of water, relying on heat to destroy harmful organisms. Bringing water to a rolling boil for at least one minute eliminates virtually all biological contaminants, including bacteria, viruses, and protozoa. The heat denatures the proteins and nucleic acids within these microbes, rendering them harmless.
This process only targets living organisms suspended in the water. Boiling water is a simple and reliable sterilization technique for freshwater sources like rivers or ponds.
The temperature required for sterilization has no effect on inorganic materials dissolved in the water. While boiling saltwater may kill any bacteria present, it leaves the high concentration of sodium chloride completely untouched. The boiling process separates pure water molecules from contaminants, but only in the form of steam.
Why Boiling Concentrates Salt
Boiling is a phase change where liquid water molecules gain enough energy to become steam. Water molecules convert into vapor and escape the container, leaving behind anything that cannot vaporize at that temperature. Sodium chloride, the primary component of salt, is a non-volatile solid with an extremely high boiling point of approximately 1,413 degrees Celsius.
Since the boiling point of salt is far greater than that of water, the salt remains in the pot as the water evaporates. As the volume of water decreases, the mass of salt stays constant, leading to a phenomenon called concentration. The final liquid remaining in the pot has a higher salt content per volume than the original saltwater, making it even saltier.
The dissolved salts, which exist as sodium and chloride ions, are too large to travel with the steam. The only way to separate the salt from the water is to collect the purified water vapor that rises from the boiling liquid. Drinking the remaining liquid is equivalent to consuming a highly concentrated brine solution.
The Health Risks of Drinking High-Salinity Water
Consuming water with an excessive salt concentration triggers a dangerous condition known as hypernatremia, meaning “too much sodium in the blood.” The human body strives to maintain a precise balance of water and salt. Introducing a high-salinity solution throws this balance into disarray.
To restore equilibrium, the kidneys must work overtime to excrete the massive influx of sodium. The kidneys use the body’s existing fresh water reserves to dilute the excess sodium, producing urine that is less salty than seawater. This process results in a net loss of water, meaning drinking saltwater paradoxically leads to increased dehydration.
The body loses more water trying to flush out the salt than was initially consumed. Symptoms of severe hypernatremia include intense thirst, confusion, muscle twitching, and seizures, as high sodium levels affect the nervous system. Sustained consumption of high-salinity water stresses the renal system and is linked to impaired kidney function and cardiovascular issues.
The Correct Survival Method: Water Distillation
The correct technique for making saltwater drinkable is distillation, which is the process of collecting and condensing purified steam. Distillation mimics the natural water cycle by forcing the water to change phase from liquid to gas and back to liquid. Because salts and other impurities cannot vaporize, the condensed steam is pure, fresh water.
A basic survival distillation setup, often called a solar still, uses heat to evaporate the water and a surface to capture the condensation. For instance, one method involves heating saltwater in a container and directing the steam onto a plastic sheet. As the vapor cools upon contact with the cooler surface, it turns back into liquid water, which is collected in a separate container.
Even a simple construction, such as a covered pot placed on a heat source with an angled collection surface, can effectively separate the water from the dissolved salts. This ensures that only pure water molecules are consumed, leaving the concentrated brine behind in the original container.