The ocean covers over 70% of the Earth’s surface. Despite this abundance, ocean water cannot be used for direct human consumption due to its high salt content, or salinity. Seawater contains an average of about 35 grams of dissolved salts per liter, far exceeding what the human body can safely process. This high concentration triggers physiological reactions that ultimately lead to severe dehydration, rendering this water source biologically unusable without significant intervention.
How High Salinity Affects the Human Body
Consuming highly saline water initiates a detrimental biological process driven by osmosis, which is the movement of water across a semipermeable membrane to balance solute concentrations. When salt water enters the digestive system, it drastically increases the solute concentration in the blood and surrounding tissues. Water then moves out of the body’s cells to dilute the bloodstream, causing cellular dehydration.
The kidneys, which regulate the body’s fluid and electrolyte balance, are then forced to work overtime to excrete the excess sodium chloride. However, the human kidney can only produce urine with a salt concentration lower than that of seawater. This means that to flush out the high salt load, the kidneys must use more water than was initially ingested, creating a net water loss.
This process accelerates dehydration, making the body thirstier and driving it toward a fluid deficit. Over time, the sustained strain on the kidneys can lead to impaired function. The resulting high concentration of salts and waste products in the blood can increase blood pressure, and untreated, this severe dehydration and organ strain can lead to kidney failure, organ damage, and death.
Other Dangerous Components Beyond Salt
While salt is the main obstacle, ocean water contains other contaminants that make it unsafe to drink. Seawater naturally contains trace minerals like copper, zinc, and iron, which are micronutrients in small amounts but can be toxic in concentrated levels. Other heavy metals, such as lead and cadmium, are also present, often accumulating from natural geological processes and human industrial activity.
The ocean is also contaminated with biological hazards, including bacteria, viruses, and protozoan cysts, frequently introduced via sewage and runoff. These microorganisms, such as E. coli, Vibrio cholera, and various enteric viruses, cause gastrointestinal illnesses, respiratory diseases, and other severe infections. Even in small quantities, these pathogens pose a serious public health risk that requires rigorous disinfection.
Human-introduced pollution further complicates water quality with contaminants like microplastics and industrial runoff. Microplastics, tiny plastic fragments, are ubiquitous in the marine environment from the breakdown of larger plastics and industrial discharge. Industrial runoff introduces persistent organic pollutants and chemicals, such as PFAS and pharmaceuticals, which are not easily removed by standard water treatment and can pose long-term health concerns.
The Process and Limitations of Purification
Ocean water can be made potable through a process called desalination, which removes the dissolved salts and minerals. The two most common methods are thermal distillation and reverse osmosis. Thermal distillation involves heating the water to create steam, which leaves the salt behind and is then condensed into pure water.
Reverse osmosis (RO) is the more widely used method, employing high pressure to force seawater through semipermeable membranes. These membranes act as an extremely fine filter, allowing water molecules to pass through while blocking salt and mineral ions. Modern RO technology is more energy-efficient than thermal processes, but still requires significant power to operate the high-pressure pumps.
The major barriers to widespread desalination are high energy consumption and the difficulty of brine disposal. Desalination plants require large amounts of energy, which contributes to greenhouse gas emissions unless powered by renewable sources. The process produces a highly concentrated salt byproduct called brine, which is typically discharged back into the ocean.
This brine is often hotter than the surrounding seawater and can contain residual treatment chemicals. It creates a dense, hypersaline plume that sinks and harms marine life near the discharge point. The high cost of energy and managing this concentrated waste stream prevents desalinated water from being a cost-effective solution for mass consumption or large-scale agricultural use globally.