Desalination is a process that removes dissolved salt and other minerals from saline water, such as seawater or brackish groundwater, to produce fresh water suitable for human use. This technology has existed in various forms for centuries, but modern techniques now provide a reliable, drought-independent water source. The central question for global water security is whether desalination can become scalable and sustainable enough to serve as a primary solution for the world’s growing freshwater needs.
The Global Imperative for Desalination
Global water demand is currently increasing at more than twice the rate of population growth, creating immense pressure on existing resources. Climate change is a major accelerant, leading to more frequent and intense droughts and unpredictable precipitation patterns worldwide. This hydrological instability severely limits the reliability of rain-fed agriculture and surface water reservoirs.
Widespread over-extraction has caused freshwater aquifers to become severely depleted, as they are being pumped faster than natural processes can replenish them. This threatens the water supply for billions of people. Additionally, in coastal areas, rising sea levels and excessive pumping cause saltwater to intrude into coastal aquifers, rendering them unusable. Desalination offers a way to bypass these constraints by tapping into the nearly limitless supply of ocean water.
Current Technical and Economic Realities
The dominant method for producing fresh water today is Reverse Osmosis (RO), which accounts for the vast majority of global production capacity. RO plants use high-pressure pumps to force saline water through specialized semi-permeable membranes. These membranes allow water molecules to pass through while physically rejecting the dissolved salts and minerals.
An alternative, older method is thermal distillation, which involves heating water to create steam, leaving the salts behind, and then condensing the pure vapor back into liquid. However, thermal plants are much more energy-intensive than modern RO systems. Even with vast improvements in membrane technology, energy consumption remains the single largest operational expense for desalination.
The specific energy consumption (SEC) for seawater RO has decreased dramatically from up to 30 kWh per cubic meter in the 1970s to approximately 3 kWh per cubic meter today. However, this still represents a substantial energy demand compared to sourcing local freshwater supplies. This high energy requirement translates directly into elevated operational costs, limiting the economic viability of large-scale desalination for many water-stressed regions. Energy costs alone can account for up to 45% of the total cost of the water produced.
Managing Environmental Byproducts
The primary non-economic challenge associated with desalination is managing the hypersaline byproduct known as brine. Modern plants generate about 142 million cubic meters of brine daily compared to 95 million cubic meters of fresh water. When this concentrated solution is discharged back into the ocean, it can significantly alter the local water column near the outfall.
The increased salinity can create localized zones that stress or kill marine organisms, potentially depleting oxygen levels in the area. Furthermore, the brine often contains residual chemicals like chlorine or antiscalants used to maintain plant operation, which can pose a toxic threat to marine life. Another environmental concern stems from the seawater intake systems that draw water into the plant.
Traditional open-ocean intakes can inadvertently harm or kill smaller organisms through impingement and entrainment. Impingement occurs when larger marine life, such as fish and crabs, are trapped against intake screens. Entrainment involves smaller organisms like fish eggs and plankton being sucked into the plant and killed. These impacts can disrupt local food webs, necessitating careful design of intake and discharge systems.
Innovations Pushing Viability
The future viability of desalination depends largely on successful technological advancements that address its two main hurdles: energy use and brine disposal. A significant area of progress involves integrating desalination facilities with renewable energy sources such as solar and wind power. Powering RO plants with green energy not only lowers the carbon footprint but also stabilizes the long-term operational costs that are vulnerable to fossil fuel price fluctuations.
Innovations in membrane technology are focused on reducing the amount of pressure, and thus energy, required for separation. Emerging materials like graphene oxide are being explored for their potential to create ultra-permeable membranes that allow water to pass through more easily. Techniques such as forward osmosis, which uses a concentration gradient instead of brute force pressure, also promise substantial energy savings and extended membrane lifespans.
Advanced brine management provides a path to minimizing environmental impact and generating revenue. Zero Liquid Discharge (ZLD) systems aim to eliminate the discharge of liquid brine entirely by evaporating all the water and recovering the solid salts. This process enables “brine mining,” where valuable minerals like lithium, calcium, and magnesium are extracted from the concentrated solution. The commercial value of these recovered minerals could offset high production costs, positioning desalination as a sustainable component of global water security.