This article details the process of desalination, an active field of water purification technology gaining promise in mitigating water crises
Seawater is so highly concentrated that drinking it will dehydrate a human being, ultimately leading to death.
But the earth is so abundant with oceans that harnessing the power of desalination—the process of converting seawater into drinkable water—has become one of the most actively scaled solutions to global water shortages.
With about 70% of the earth's surface covered in mostly seawater, it is no wonder that governments, NGOs, and private companies are exploring ways to make desalination a more widespread method of water purification.
It's a very promising frontier in the water purification space, but it's not without its challenges.
What is Desalination?
Desalination is the process of converting seawater into drinkable water by removing the salt content. The technology behind the desalination process is continually being innovated, but there are three main methods that are particularly worth covering.
Thermal Desalination
Thermal, or flash, desalination is a type of distillation method that extracts potable water from seawater through the process of evaporation. Intense heat is used to convert seawater into steam, condensing the steam into clean water and leaving the concentrated salt brine behind.
Some of the challenges of thermal desalination are its high oil consumption necessary to maintain heat and the large amounts of salt-heavy brine left behind as a byproduct, often requiring more energy to be pumped back into the ocean.
While thermal desalination is the earliest method of desalination, there has been a significant shift toward more energy-efficient methods of desalination due to its high energy demands and excessive byproducts.
Reverse Osmosis
Membrane purification technology—predominately reverse osmosis—is currently the premier method of desalination due to its effectiveness and lower energy costs. Reverse osmosis works by using water pressure to pass seawater through a molecular membrane where only the H₂O molecule can fit, leaving all the salt compounds behind.
While reverse osmosis is much less energy-intensive than thermal desalination, it still requires large amounts of electricity and revenue to maintain.
Electrodialysis Reversal
Electrodialysis Reversal, or EDR, is a method that uses electrical nodes to attract and capture charged salt particles, leaving only clean water.
While EDR is a promising venture for desalination, its high electricity requirements present a challenge.
Challenges and other factors
The type of desalination method used largely depends on factors such as cost, energy availability, infrastructure, and the salinity of the water source. The ongoing challenge for desalination technology is the energy and cost required to maintain the process, especially for large community applications.
Can Desalination Solve the Water Crisis?
With nearly half of the world's population currently living in water-stressed areas, desalination is proving to be a major help to the growing problem of water scarcity.
About 20,000 desalination plants are currently in operation worldwide, with the Middle East and Asia-Pacific regions experiencing the most growth. The largest desalination plant is in Ras Al Khair, Saudi Arabia, and produces 1,036,000 cubic meters, or 273 million gallons, per day.
The United States also has several active desalination plants, the largest in Carlsbad, CA, capable of producing 50 million gallons of clean water per day and responsible for 7% of San Diego County's water.
Altogether, a total of 177 countries are currently running desalination plants, providing a cumulative amount of 95 million cubic meters of freshwater per day. While still far from perfect, desalination technology looks to be the common area where most countries around the world are focusing their attention on the pursuit of water sustainability.
Future of Desalination Technology
As water engineers and scientists explore innovative ways to improve desalination, new methods, such as solar desalination, nanofiltration, and graphene desalination are emerging.
Solar desalination
Solar desalination involves harnessing the sun as a power source to solve the energy-intensive process of desalination. Neom, a 26,500 km-long smart city being constructed in Saudi Arabia is projected to use solar desalination technology to purify its water.
Nanofiltration
Nanofiltration is similar to reverse osmosis but constructs the membrane of special materials allowing for even smaller pore size, essentially small enough for only the H₂O molecule. Its use in desalination is currently an area of rigorous study.
Graphene desalination
Graphene is a special arrangement of carbon atoms that allows for very innovative technological processes and is a promising component for the future of desalination. Graphene membranes may allow for more efficient desalination mechanisms than traditional reverse osmosis membranes.
Small-scale Desalination for Home
While desalination is a frontier prominent on the world stage, individuals can experience the benefits themselves through small-scale desalination devices.
Most homes on city water or well water don't need a dedicated desalination unit — a standard home water filtration system or reverse osmosis filter handles the contaminants typical residential water sources contain. Home desalination makes practical sense primarily for off-grid coastal locations, boats, and emergency preparedness where the water source is seawater or highly brackish water.
Companies such as Quench Sea and Rainman make portable desalination devices that can be used for small-scale applications.
QuenchSea
QuenchSea is a portable desalination device that uses reverse osmosis to convert seawater to drinkable water at a rate of 4 Liters or 1 Gallon per hour. The device is ultralight and requires no electricity to operate. The RO membrane itself will last between 6 to 12 months and produce up to 1,000 liters of fresh water before needing replacement.
Rainman Water Maker
The Rainman AC is a portable desalination unit that also uses reverse osmosis technology but incorporates the use of electrical power, producing up to 140 liters (37 gallons) of fresh potable water per hour.
Power comes in 230VAC/50Hz or 115VAC/60Hz options and is designed to run off of a minimum of a Honda 2kW generator.
Cost of Desalination
Desalination is more expensive than treating conventional freshwater sources. Treating river or groundwater typically costs $0.05–$0.15 per cubic meter. Seawater reverse osmosis at a large municipal plant currently costs $0.50–$1.00 per cubic meter — roughly five to ten times more.
Energy accounts for the largest share of that cost, typically 30–50% of operating expenses. Seawater reverse osmosis requires about 3–4 kWh per cubic meter of water produced. That's a significant improvement from older thermal desalination plants, which consumed 7–15 kWh per cubic meter, but it remains the central economic challenge for large-scale desalination.
Capital costs are substantial. The Carlsbad Desalination Plant in California — the largest in the US at 50 million gallons per day — cost approximately $1 billion to build. The water it produces sells to the San Diego County Water Authority at roughly $2,000 per acre-foot, compared to about $700 per acre-foot for imported water.
Costs have dropped significantly over the past two decades as membrane technology improves and more renewable-powered plants come online. But desalination remains a premium water source — appropriate for water-scarce regions where conventional alternatives are exhausted, not a cost-effective replacement for existing freshwater infrastructure where those resources still exist.
Environmental Impact of Desalination
Desalination's primary environmental concern is brine disposal. For every liter of fresh water produced, a seawater reverse osmosis plant generates roughly one liter of concentrated brine — approximately twice the salt concentration of the source water. Most coastal plants discharge this brine directly into the ocean near the facility. At high concentrations without adequate mixing, dense brine sinks and can displace oxygen near the seafloor, affecting bottom-dwelling marine life.
Energy consumption is the second major concern. A plant powered by fossil fuels carries a significant carbon footprint: a facility producing 100 million gallons per day and consuming 3–4 kWh per cubic meter generates roughly 400,000–500,000 tons of CO₂ annually on coal or natural gas. This is why solar-powered and renewable-integrated plants — including Saudi Arabia's NEOM project — represent the direction the industry is moving.
Intake infrastructure can also affect marine life. Open-ocean intake systems can trap or kill small fish, larvae, and invertebrates at the screen. Subsurface intake systems (beach wells or infiltration galleries) largely eliminate this risk and are increasingly preferred for new facilities where the geology allows it.
The environmental trade-off comes down to siting, brine diffuser design, and energy source. In water-scarce regions where aquifer depletion and drought are the alternative, a well-managed desalination plant with renewable power and subsurface intake can have a smaller footprint than the status quo.
Desalination is one of the most significant technologies being developed to expand the global freshwater supply, but it remains energy-intensive and expensive at scale. For most households, a standard water filtration system is the practical choice — desalination is relevant when the source water is seawater or highly brackish water that standard filters can't treat.
To understand the broader challenge desalination addresses, see water scarcity facts and the global water crisis.
Desalination FAQs
What is desalination?
Desalination is the process of removing salt and other dissolved minerals from seawater or brackish water to make it safe to drink. The two dominant methods are reverse osmosis, which forces water through a semi-permeable membrane that blocks salt, and thermal (flash) distillation, which evaporates water and condenses the salt-free steam.
What are the main methods of desalination?
There are three primary methods: thermal desalination (distillation using heat to evaporate and condense water), reverse osmosis (membrane filtration under pressure — now the most widely used method), and electrodialysis reversal (EDR) (using electrical charge to pull salt ions out of the water). Emerging approaches include solar desalination, nanofiltration, and graphene membranes.
Is desalinated water safe to drink?
Yes. Desalinated water produced by a properly operated plant meets the same drinking-water safety standards as conventional supplies. Because the process removes nearly all minerals, most plants add a remineralization step to restore taste and balance before the water is distributed.
Why is desalination so expensive?
Energy is the main cost — seawater reverse osmosis uses about 3-4 kWh per cubic meter, making desalinated water roughly five to ten times more expensive than treating conventional freshwater. Large capital costs (the Carlsbad plant in California cost about $1 billion) and brine disposal add to the expense, which is why desalination is used mainly in water-scarce coastal regions.
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