The Earth’s oceans hold the vast majority of our planet’s water, a potential resource for human consumption. However, this water is naturally saline, containing high concentrations of dissolved salts that make it unsuitable for direct drinking. The challenge is safely removing these salts to make ocean water potable, a process known as desalination.
Why Direct Consumption is Harmful
Drinking ocean water directly poses significant health risks due to its high salinity. Seawater typically contains about 3.5% salt, a much higher concentration than the human body can safely process. When consumed, this excess salt enters the bloodstream, increasing its solute concentration.
The human kidneys filter waste products and maintain the body’s fluid balance. To excrete the large amount of salt ingested from seawater, the kidneys must produce urine saltier than the body’s normal fluids. This process requires the kidneys to draw water from the body’s cells and tissues through osmosis.
As a result, drinking seawater leads to a net loss of water from the body, causing severe dehydration. Symptoms can include muscle cramps, dry mouth, nausea, and delirium. Prolonged consumption can overwhelm the kidneys, potentially leading to kidney failure, coma, and ultimately, death, as the body’s cells shrivel from water depletion.
Methods for Desalination
Making ocean water potable primarily involves desalination, with two main methods: distillation and reverse osmosis. Distillation is a thermal process that mimics the natural water cycle. Saline water is heated to produce steam, leaving salts and other impurities behind. The steam is then collected and condensed into fresh, desalinated water.
While feasible for small-scale or survival situations using improvised setups, traditional distillation is energy-intensive due to the heat required to boil water. Multi-stage flash (MSF) and multiple-effect distillation (MED) are forms that improve energy efficiency by reusing heat.
Reverse osmosis (RO) is a membrane-based process that has become the most common method for large-scale desalination due to its efficiency. It works by applying high pressure to saline water, forcing it through a semi-permeable membrane. This membrane allows water molecules to pass through but blocks larger salt ions and other dissolved impurities. RO systems are highly effective, capable of removing up to 99% of salts and other contaminants. The process requires significant pressure, typically between 40 to 82 bar (600-1200 psi) for seawater, to overcome the natural osmotic pressure.
Practical Considerations and Limitations
Desalination, regardless of the method, comes with practical considerations and limitations, particularly regarding energy consumption. Both distillation and reverse osmosis are energy-intensive processes. For instance, reverse osmosis plants typically consume 3 to 6 kilowatt-hours (kWh) per cubic meter of water produced. This energy demand translates into substantial operational costs, with energy often accounting for a significant portion of total operating expenses, sometimes as much as 36%.
Beyond salt removal, desalinated water may still contain other impurities. While reverse osmosis membranes are effective at blocking dissolved salts, bacteria, and even microplastics, additional purification steps might be necessary for other contaminants. Large-scale desalination plants are complex facilities that provide municipal water to vast populations, with construction costs for a typical large plant ranging from tens of millions to over a billion dollars.
In contrast, improvised desalination methods for individual survival are severely limited in their output. While theoretically possible to distill water in an emergency, the amount of fresh water produced is minimal, and the process is slow and demanding of resources like fuel. Relying on desalination in a survival context is generally a last resort due to the equipment, energy, and time constraints involved.