Seawater can be made drinkable, but the process requires significant energy and technological intervention to remove the vast amount of dissolved salts. The Earth’s oceans hold approximately 97% of all water on the planet, making the ability to convert this resource into potable water a key strategy for addressing global water scarcity. Modern desalination methods successfully separate pure water molecules from dissolved minerals, yielding fresh water that meets drinking standards.
The Core Problem: Why Seawater Is Dangerous
The danger of drinking seawater is rooted in osmosis, a natural process governing water movement across semi-permeable membranes. Seawater contains an average salinity of about 35,000 parts per million (ppm), or 3.5% dissolved salts, which is roughly four times saltier than human body fluids. When ingested, this hypertonic solution dramatically raises the blood’s salt concentration.
To equalize this concentration, the body’s cells release their water reserves to dilute the surrounding fluid, causing cellular dehydration. The kidneys compound this issue because they can only produce urine slightly less salty than the blood. To excrete the salt load, the kidneys must draw even more fresh water from the body’s reserves, resulting in a net loss of water. This accelerating cycle of dehydration quickly leads to organ failure and death.
Industrial Solutions: Reverse Osmosis
The most widespread industrial method for desalination is Reverse Osmosis (RO), a pressure-driven process. The process begins with extensive pre-treatment, filtering the raw seawater to remove solids and microorganisms that could clog the membranes. High-pressure pumps then apply immense force to the water, typically between 50 and 60 bar for high-salinity water.
This pressure exceeds the natural osmotic pressure of the saltwater, forcing water molecules through a semi-permeable membrane. These membranes have microscopic pores large enough for water molecules to pass through but small enough to reject dissolved salt ions like sodium and chloride. The process separates the feed water into two streams: purified, low-salinity product water, and a concentrated, hypersaline stream called brine. Modern RO plants typically convert around 40% of the incoming seawater into potable water, leaving the remaining 60% as brine concentrate.
Survival Techniques: Distillation and Solar Stills
For emergency or small-scale applications, desalination can be achieved through distillation, which mimics the natural water cycle. This process involves heating seawater until it evaporates, leaving all non-volatile impurities like salt and heavy metals behind. The resulting water vapor is captured and cooled, causing it to condense back into pure liquid water.
A solar still is a low-tech device that utilizes this principle, relying entirely on the sun’s energy. A simple still is constructed by placing saltwater inside a sealed box covered with a sloping clear sheet. Solar radiation heats the seawater; the vapor rises, condenses on the cooler cover, and runs into a collection trough. While effective at purifying water, these passive devices are extremely slow and yield very low volumes, often producing only a few liters per day.
Global Implementation and Cost
The widespread adoption of desalination is constrained by the high energy requirements of the industrial process. Although reverse osmosis is more efficient than older thermal distillation methods, it still demands significant electrical input to power the high-pressure pumps. This energy demand contributes to the high cost of desalinated water compared to traditional fresh water sources.
A second major challenge is managing the brine byproduct, a liquid concentrate with salinity up to twice that of the original seawater, often containing pre-treatment chemicals. For every liter of fresh water produced, approximately 1.5 liters of this hypersaline brine are created and must be disposed of. When discharged back into the ocean, this dense effluent can sink and raise the salinity and temperature of the surrounding water. This poses a serious threat to local marine ecosystems, particularly sensitive habitats like coral reefs.