Desalination is the process of removing salt and other dissolved minerals from seawater or brackish water to produce fresh water suitable for human consumption, agriculture, or industry. This technology is increasingly used in water-scarce regions to create a climate-independent supply. While desalination offers a solution to the growing global freshwater crisis, the process generates substantial environmental and economic burdens. Understanding these drawbacks, from massive energy demands to concentrated waste disposal, is essential for evaluating the long-term sustainability of this water production method.
Massive Energy Consumption and Climate Impact
The operational requirements of desalination plants place a significant strain on energy resources, directly contributing to greenhouse gas emissions and climate change. Seawater reverse osmosis (RO), the most widely adopted method, works by forcing water through semipermeable membranes under high pressure to separate the salt. This mechanical separation is extremely energy-intensive compared to traditional water treatment methods.
Modern large-scale RO facilities typically require between 2.5 and 4.0 kilowatt-hours of electricity to produce one cubic meter of fresh water. Although technological advances have reduced this intensity significantly since the 1970s, the power needed for a single plant can rival that of a small city. In many regions, this electricity is sourced from fossil fuels.
The reliance on fossil fuels creates a large carbon footprint for every gallon of water produced. Unless desalination facilities are powered entirely by dedicated renewable energy sources, they contribute substantially to the climate crisis. This inherent energy intensity makes the process a less sustainable option than water conservation or reuse initiatives.
Brine Effluent and Marine Ecosystem Toxicity
The most direct and localized environmental harm from desalination is the discharge of the concentrated waste product known as brine. For every volume of fresh water created, a larger volume of hypersaline brine is produced, which is often twice as salty as the original source water. Standard seawater typically has a salinity of about 3.5%, meaning the brine effluent can be concentrated to 7% or higher.
This effluent is not simply over-salted water; it also contains concentrated residual treatment chemicals used during the desalination process. These can include chlorine derivatives, anti-scalants to protect the membranes, and heavy metals like copper or nickel leached from the plant’s equipment. When discharged back into the ocean, this dense, warm, and chemically altered brine sinks rapidly to the seabed, creating a dense layer that is slow to disperse.
The resulting hypersaline plume can severely damage or destroy benthic habitats, such as seagrass beds and coral reefs, which are highly sensitive to changes in salinity. Organisms that live on or near the sea floor, including various invertebrates and fish eggs, suffer osmotic stress and can die due to the inability to regulate their internal salt balance in the unnaturally concentrated water. Furthermore, the chemicals within the brine can be toxic to marine life, disrupting local food webs and creating localized “dead zones” around the outfall pipe.
Another significant ecological impact occurs at the water intake stage, where massive volumes of source water are drawn into the plant. This intake process can result in the “entrainment” of microscopic marine life, such as plankton and fish larvae, which are sucked into the system and killed. Larger organisms can become “impinged” against the intake screens, resulting in injury or death, ultimately depleting the local marine population and affecting the broader ecosystem.
Extreme Financial Costs and Infrastructure Dependency
The financial investment required for desalination is exceptionally high, which translates directly into increased costs for consumers. Building a large-scale seawater reverse osmosis facility requires a massive Capital Expenditure (CAPEX), often ranging from $1,000 to $2,500 per cubic meter of daily production capacity. This initial outlay covers the complex intake and outfall infrastructure, the specialized membrane systems, and the energy recovery devices.
Once operational, the facilities face high Operational Expenditure (OPEX), largely dominated by the cost of electricity. Energy typically accounts for 30% to 40% of the total operating costs, linking the financial viability of the plant directly to volatile fossil fuel markets. Other recurring expenses include the periodic replacement of expensive membranes, which have an average lifespan of three to five years, and the purchase of specialized treatment chemicals.
These substantial financial burdens mean that desalinated water is often two to four times more expensive than water from conventional sources like reservoirs or groundwater. The high operational complexity also creates a significant infrastructure dependency; these plants require highly specialized labor for maintenance and are vulnerable to power outages, equipment failure, or natural disasters. The long-term commitment to such expensive and complex infrastructure can lock municipalities into a costly water source, limiting investment in less energy-intensive alternatives.