Almost a quarter of the world's population holsters with water for drinking. sea water can be processed at a cost of half a dollar per cubic meter, but this is still rarely done.
Methods of obtaining drinking water from salt water have been known for more than two millennia. Greek sailors in ancient times boiled sea water, and in ancient Rome it was filtered through clay pipes to make it drinkable.
Modern forms of ancient technologies are "the present and the future of solving water scarcity," said Manzoor Qadir, deputy director of the United Nations University's (UNU) Institute for Water, Environment and Health.
Salt water everywhere, but no drinking water
About 70 percent of the Earth's surface is covered by water, but of this more than 1,4 trillion liters, less than three percent is fresh water, and less than one percent can be used as drinking water.
These resources are becoming increasingly scarce. The world population is growing and in many places there is not enough fresh water. More and more droughts due to climate change are leading to water shortages in more and more regions.
A quarter of people already live in countries with "extreme water scarcity". This means that at least 80 percent of all available water is used there every year. This increases the risk of water shortages and temporarily forces governments to severely restrict supplies.
An additional billion people could suffer from extreme water scarcity by 2050, even if global warming can be limited. Even optimistic climate scenarios show this.
Desalination is a growing industry
Despite criticism for its cost, high energy consumption and environmental impact, desalination has been a booming industry for the past two decades.
"Increasing water scarcity is driving this development," Kadir says. "More and more desalination plants are being built."
Modern desalination plants remove salt either by thermal distillation, heating seawater and capturing water vapor, or they work with so-called reverse osmosis, in which water is forced through filter membranes.
Alternative methods of sweetening can also play an important role, Kadir says, including artificially producing rain by seeding clouds, harvesting water from fog, transporting icebergs to dry areas or recycling water. But these methods would not be able to produce enough water to meet global demand.
Currently, desalination produces 56 billion liters of drinking water per day. That's about seven liters for each of the eight billion people on Earth.
Of the estimated 16.000 desalination plants worldwide, about 39 percent are in operation in the Middle East. Next to North Africa, this is the most water-poor region in the world.
A future without desalination plants would be "almost impossible" for many countries, Kadir explains, because there is very little rainfall there.
Worldwide, only about half a percent of total freshwater consumption is covered by desalination plants. However, this percentage is much higher in countries such as Qatar (76 percent) and Bahrain (56 percent).
More and more energy efficient technologies
Desalination plants use a lot of energy. Until now, they have mainly operated on fossil fuels such as oil or coal and are therefore harmful to the climate.
On the dry Mediterranean island of Cyprus, about 80 percent of drinking water is obtained through desalination. A 2021 study found that four desalination plants consume a total of five percent of electricity and are responsible for about two percent of greenhouse gas emissions.
Increasing energy efficiency is one of the factors driving industry growth, said Hugo Birch, desalination and water reuse editor at Global Water Intelligence, an information platform for desalination.
Most new desalination plants use reverse osmosis rather than thermal processes, which are more energy efficient, Birch said. The change could cut electricity costs in half.
According to one estimate, the energy required for reverse osmosis desalination fell by nearly 90 percent between 1970 and 2020. Some forecasts suggest that technological advances will reduce desalination costs by an additional 60 percent over the next two decades.
Poor countries cannot afford the plants
The cost of producing desalinated water has dropped significantly – to about half a dollar per cubic meter. But this is "still a job for rich countries," says Kadir. "The main problem remains that it is still not affordable for low-income countries."
Over 90 percent of desalination to date takes place in middle- and high-income countries. According to forecasts, by 2050 especially poorer countries, such as African countries south of the Sahara, will become "hotspots" of water shortages.
Smaller solar or wind power plants for desalination that are independent of the electricity grid are also being developed. But Kadir doesn't believe it reaches the marginalized neighborhoods and communities that need them the most.
Saltwater waste threatens marine ecosystems
One of the biggest environmental problems associated with desalination is the release of the resulting brine into the environment. This can lead to "pollution of the sea, groundwater and soil salinization," explains Argiris Panagopoulos, a chemical engineer at the National Technical University of Athens.
About 70 percent of the world's saltwater waste is in the Middle East. According to Birch, the main reason for this is that the desalination plants there mostly use very salty seawater. In other regions, such as the USA, less saline water is often used.
Birch adds that the plants usually have a built-in mechanism that distributes the waste so that the brine does not concentrate in one place.
Now new technologies are being developed for the processing of salt water. Panagopoulos explains that they can help reduce pollution from desalination plants and recover valuable materials such as minerals, salts and metals.
A sustainable future for desalination?
But there is still room for improvement, such as handling salt water and switching to renewable energy, the engineer said.
"Desalination has made significant progress in recent years, but there are still some challenges to overcome until it becomes environmentally sustainable," says the chemical engineer.
But in any case, desalination will play a key role in solving future water shortages, Manzoor Kadir from UNU is convinced. "Whether it rains or is dry, there is sea water. That's the best thing about desalination."
