Water scarcity is affecting increasing number of countries. The crisis is driven by several factors, including rising aridity due to climate change and substantial population pressure, particularly in coastal areas (40% of the world’s population lives within 100 km of the coast). According to the UN, by 2030, the world’s population will face a 40% water deficit. This problem stems from the fact that only 0.5% of available water is potable and easily accessible;¹ the rest being saltwater from seas and oceans. This critical challenge is compounded by rapid population growth and the effects of climate change. There are limited alternatives: reducing consumption (difficult given unmet needs in many regions), developing new resources (dams, aquifers), or optimizing the use of existing resources (recycling). Paradoxically, water is abundant on Earth, but mainly in saline form (oceans, seas). In this context, seawater desalination appears to be a promising solution, allowing the exploitation of virtually unlimited water resources.

Seawater desalination is a process that removes salt from salty or brackish water to make it potable or use it in irrigation. However, according to WWF (World Wide Fund for Nature), this solution can have a negative impact on the environment due to the composition of the discharge generated by this process, which can alter seawater parameters and negatively affect underwater flora and fauna. The discharge generated by the desalination plant generally comes in the form of brine containing various salts and organic compounds.

The sector is booming, with annual capacity growth of 6 to 12%, with more than 21,000 desalination plants operating worldwide by 2022.² However, the intensive use of fossil fuels for desalination poses a major challenge. Currently, only 1% of desalination plants are powered by low-carbon energy sources. Faced with this reality, innovation in green desalination processes is becoming essential. While desalination offers interesting prospects, significant obstacles remain: its high economic cost and its environmental impact.

1. Desalination: The Solution to Eradicate Global Water Scarcity

The age-old concept of seawater has its roots in the necessity for clean drinking water. But it is only recently that this technique has reached a distinctly industrial stage to meet an exponential demand, notably due to the evolution of human consumption per capita. The logic is well established, even if the exact figures are disputed: 72% of the total surface of the Earth is covered with water, but 97.5% of this water is salty. The remaining 2.5% represents fresh water from glaciers and snow, rivers, lakes and groundwater. This still leaves 12,500 km3 available, but this figure has remained constant over time, so the theoretical water resource per capita continues to decline. In 1950, it represented 16,800 m3 /inhabitant, then 12,290 m3 /inhabitant in 1970. In 1995, with 6 billion inhabitants, this fell to 7,600 m3, a decrease of 37%. In 2009, it was at 6.8 billion inhabitants and 6,500 m3 and only 4,800 m3 are in 2025.

Could our seas be the solution to our water scarcity problems in the face of severe drought and a growing population? The development of sustainable seawater desalination technology could play a crucial role in solving the global water shortage. The oceans cover more than 70% of the Earth’s surface and contain more than 96%[1] of the planet’s water resources. The main problem with seawater is that it is unfit for human consumption. It is saturated with salt and other minerals. Desalination involves transforming salty seawater into potable water. Is desalination the magical remedy that will provide our planet, with its over 7 billion inhabitants, access to clean water? Will it help us overcome the devastating effects of severe drought and worsening climate change?

1.1 Definition of desalination 

Desalination is a process that removes salinity, harmful chemicals, and other impurities from salty or polluted water, converting it into water suitable for drinking or use in agriculture and industry. The desalination process relies on a variety of technologies, such as reverse osmosis, distillation, multiple evaporation, solar desalination, and others.

It requires significant energy and financial resources. Desalination is an important solution to overcome freshwater shortages in many regions of the world, but it also requires attention to the associated environmental and economic impacts.

1.2 Types of water desalination plants

– Reverse Osmosis (RO): These plants use a semi-permeable membrane to separate salinity and impurities from the water. Water is passed through the membrane at high pressure to separate chemicals and impurities from the pure water.

– Distillation Plant: The distillation process heats water, converts it to steam, and then condenses the steam again to produce pure water. The pure water is then separated from the impurities and chemicals.

– Multiple Effect Evaporation Plant (MEE): The process uses multiple evaporations to evaporate water and condense the steam to produce pure water. This process involves several successive evaporation stages to increase the efficiency of the process.

– Solar Desalination Plant: Solar energy is used to desalinate water by heating it with solar energy, then condensing the steam and collecting it to produce pure water.

These are some common types of desalination plants, each of which differs in the method they use to convert salty or polluted water into pure water suitable for drinking or other applications.

2. Desalination costs

Globally, approximately 1% of drinking water is desalinated, while global water consumption, including industrial and agricultural uses, reaches approximately 2.5 billion cubic meters.

In recent years, the desalination sector has become more competitive due to increased financial liquidity and maturing financial markets.[2] Desalinated water prices entering distribution networks vary widely globally, ranging from US$0.50 to US$2.50 per cubic meter for seawater desalination and US$0.60 to US$2 per cubic meter for brackish water desalination.[3] This depends on several factors, such as the capacity and type of desalination plant, the source of raw water (seawater or brackish water), labor, location, and the type of energy used, whether conventional or renewable.

In addition, the proximity of plants to end users significantly impacts costs, as transporting treated water long distances inland requires the use of large-diameter pipes, booster pumps, and storage tanks, increasing capital infrastructure costs and operating electricity costs. Recent large-scale desalination projects highlight the significant costs of transporting water inland. For example, the Carlsbad desalination plant in San Diego County, which produces 190,000 cubic meters of water per day, required approximately US$1 billion. Even shorter distances carry significant costs. The Melbourne desalination plant in Australia faced a cost of US$750 million to extend an 85-mile pipeline to Monterrey, Mexico. Regardless of the distance, transportation imposes significant financial burdens, such as the US$140 million spent to build a 25-mile pipeline.

In contrast, traditional freshwater sources remain much less expensive. River and lake water costs between US$0.10 and US$0.50 per cubic meter, groundwater and well water cost between US$0.30 and US$1.00, rainwater harvesting costs between US$0.15 and US$1.50, and wastewater recycling costs between US$0.30 and US$1.15.

Consequently, the cost of desalinated water remains 1.5 to 4 times higher than that of most traditional freshwater sources, such as lakes, rivers, and shallow wells.

In the Middle East, Saudi Arabia and the United Arab Emirates are among the least expensive destinations for desalination, thanks to relatively low energy prices and economies of scale at their large facilities. Increasing reliance on renewable energy to power desalination operations could further reduce costs. Already, the cost of water produced from Saudi Arabia’s most recent projects is around $0.50 per cubic meter, supported by the low cost of solar energy and government subsidies for fossil fuels.[4]

In 2020, Dubai Electricity and Water Authority (DEWA) announced that the Hassyan Reverse Osmosis (RO) desalination plant, with a production capacity of 545,000 cubic meters per day, would deliver water at a record-breaking cost of US$0.306 per cubic meter when it comes online in 2023, making it the lowest unified water tariff in the world to date. This achievement is attributed to the efficiency of RO technology and the adoption of best practices in desalination.

Table 1: Capital and operating expenses for large seawater reverse osmosis desalination plants

Source: Spanish Association for Desalination and Reuse of Water, Amsterdam. Accessed July 16, 2024.

2.1 Expensive technology

Large-scale desalination plants are expensive. Investments in large-scale plants typically run into the hundreds of millions of dollars. Unsurprisingly, the majority of recently built plants are located in prosperous countries such as the UAE and Israel or were designed to supply major cities in Australia or the United States.

According to the latest market study by Global Industry Analysts, a research firm, the global desalination market is expected to grow at a compound annual rate of 9.8%, with an expected increase from US$15.2 billion in 2022 to US$22.5 billion in 2026.[5]

Desalination also places a significant burden on countries that produce desalinated water. This depends on the conditions and the technology used: the U.S. Department of Energy’s recommendations advise managers to aim for $1.50/m³ for highly saline water, such as brine derived from oil and gas operations, and $0.50/m³ for low-salt water, such as seawater.

2.2 Desalination: massive use of energy 

Theoretically, desalinating one cubic meter of moderately saline water, under isentropic conditions and at a constant temperature, requires a minimum amount of energy estimated at only 536 Wh. However, in practice, the two main desalination methods currently used are much more energy-intensive, consuming between 5 and more than 30 times this ideal value. Distillation, a thermal process that involves heating salt water until it evaporates to recover fresh water through condensation, has an energy consumption of approximately 15 kWh per cubic meter of desalinated water. In contrast, reverse osmosis, which uses pressure to force salt water through a semi-permeable membrane, is considerably more efficient, with energy consumption potentially reduced to between 2.5 and 3 kWh per cubic meter.

Theoretically, desalination—whether by reverse osmosis or distillation—requires a minimum of 1 kWh[6] per cubic meter of water produced. However, in practice, this value is largely exceeded due to additional requirements: seawater pumping, distribution, brine discharge (which vary depending on the location), as well as pretreatment and remineralization (which depend on the quality of the source water).

Today, reverse osmosis, the most widely used technology, consumes on average:

• 2 kWh/m³ for the desalination process alone
• Up to 4 kWh/m³ for a complete installation (including pretreatment and distribution)

In comparison, thermal distillation, which is more energy-intensive, generally requires between 5 and 15 kWh/m³, making it less competitive in the context of rising energy costs. This difference explains why reverse osmosis dominates the market, representing nearly 70% of global capacity by 2024, compared to approximately 25% for thermal processes (MED, MSF) and 5% for other technologies (electrodialysis, etc.).

Its widespread adoption is particularly noticeable in non-oil and gas-producing countries (such as Spain and Chile), where energy efficiency is crucial. Conversely, the Gulf countries, which have abundant and inexpensive fossil fuels, still widely use distillation, particularly for very large installations coupled with power plants.

Desalination contributes to greenhouse gas emissions, particularly through its energy use. Globally, reverse osmosis desalination is estimated to use 100 TWh[7] of electrical energy per year, equivalent to approximately 0.4% of global electricity consumption. It is estimated that it emitted 76 million tons of CO2 in 2014, with an estimated 400 million tons of CO2 expected by 2050.

3. Desalination and its environmental impact

Desalination technology plays a vital role in the search for fresh water, particularly in arid and coastal regions. A United Nations-backed study[8] has revealed that nearly 16,000 desalination plants worldwide are producing higher-than-expected quantities of brine (wastewater) and toxic chemicals, posing a threat to the environment. To produce 95 million cubic meters of drinking water, desalination plants also produce 142 million cubic meters of brine each day, a 50% increase over previous estimates.

The study, conducted by the Canada-based United Nations University Institute for Water, Environment, and Health, shows that approximately 55% of the brine is produced by seawater desalination plants in Saudi Arabia, the UAE, and Qatar.

The wastewater, which is 5% salt, often contains toxic substances such as chlorine and copper used for desalination. Globally, the salt content of seawater is approximately 3.5%. Edward Jones, lead author of the study and a researcher at Wageningen University in the Netherlands, said that chemical waste “accumulates in the environment and can have toxic effects on fish.” He added that waste from highly saline waters can reduce the oxygen content of seawater near desalination plants, with “significant impacts” on oysters, crabs, and other deep-sea creatures, leading to “ecological impacts observable at all levels of the food chain.”

Figure 1 : Environmental impact of desalination

Source: https://drrajivdesaimd.com/2024/05/07/desalination

3.1 Desalination and climate issues

Seawater desalination is sometimes presented as a miracle solution to the problem of drinking water scarcity. In addition to the fact that it remains financially inaccessible to poor countries (in terms of income or oil), these technologies remain energy-intensive, and the question of their environmental impact is far from resolved. Too often, the installation of desalination facilities is a way to circumvent glaring problems of waste or poor water governance and to sidestep necessary reforms.

Today, water resources oscillate between extremes. On the one hand, cyclones, floods, and other climatic events bring it to an overabundance. On the other hand, droughts and desertification lead to crippling shortages and miserable living conditions for populations. This conflict between scarcity and abundance exists everywhere on Earth, from developed to developing countries.

Although the energy efficiency of desalination techniques, particularly reverse osmosis, is constantly improving, these processes are still major energy users. The major environmental problem stems from the fact that most of this energy is generated by the combustion of fossil fuels, resulting in the emission of various atmospheric pollutants, notably carbon dioxide (CO2), sulphur and nitrogen oxides, as well as fine particles. As a concrete example, it was estimated in 2007 that the Spanish desalination production system emitted 680 grams of CO2 per cubic meter of desalinated water. Considering the millions of cubic meters of desalinated water produced worldwide every day, this translates into thousands of tons of CO2 emitted into the atmosphere every day, a significant contribution to the greenhouse effect and global warming that must be taken into account in the current environmental context.

3.2 Marine organisms collide with sieve drums

The water withdrawal devices installed by desalination plants are not without impact on local ecosystems. To prevent debris or large organisms from entering the plant’s water system, sieve drums (sampling structures) with an average mesh size of 5 mm are placed between the intake device and the feed pumps.

Marine organisms such as fish can collide with these drums and injure themselves (scaling, orientation problems, etc.). These physical problems can lead to increased mortality due to disease and increased predation.

3.3 Impacts of discharge

Discharges from desalination plants, known as effluents, have environmental impacts mainly linked to their high salt concentration (brine), with the addition of chemicals and a potentially high temperature to a lesser extent. To mitigate these impacts, these discharges are regulated by the “Telluric” protocol of the Barcelona Convention, to which many Mediterranean countries (including France, Spain, Egypt, Lebanon and Libya) adhere. This convention imposes limit values for discharges (salt, chlorine, temperature, etc.) and requires an environmental impact study prior to any plant construction.

The most notable characteristic of these effluents is their high salinity. For plants using the thermal process, the conversion efficiency is around 10%, which means that the discharged water is on average 10% more concentrated in salt than the feed seawater.[9] However, these discharges are often diluted by half with cooling water, reducing their salt concentration to just 5% more than natural seawater. On the other hand, membrane process plants (reverse osmosis) produce wastewater with a significantly higher concentration, ranging from 30% to twice the concentration of the original seawater. The direct discharge of undiluted, untreated brine from desalination plants results in a localized increase in salinity in surrounding areas. For example, observations have shown that discharges from plants in the Arabian Gulf raise salt concentrations by 5 to 10 g/L, compared with a regional average of 45 g/L.[10] This excessive effluent salinity is the main source of impact on marine ecosystems. Indeed, brine discharge creates a stratification of water layers, with the saltiest and densest accumulating at the bottom, disrupting exchanges and mixing between surface and bottom waters. In certain situations, depending on local marine currents, up to 40% of the discharge area can be covered by this saline concentration.

According to UN estimates, 95 million cubic meters of desalinated water and 140 million cubic meters of brine are produced daily worldwide.[11] It is important to consider the physical and chemical properties of brine, which are influenced by feed water quality, pretreatment methods, desalination technology, and recovered water rates. While reverse osmosis (RO) processes produce brine with higher salinity but the same temperature as ambient water, multistage desalination (MSF) produces brine with higher temperature and salinity but generally lower salinity than RO. Hybrid desalination processes, which combine RO and thermal technologies, provide a more sustainable process by heating the high-salinity RO brine and reducing the brine temperature using MSF or multi-effect distillation (MED) technology.[12]

Although desalination is a major concern for desalination technologies, it is important to note that exploitation of inland water resources and desalination result in a harmonious balance between real water and salinity. Excess water withdrawn for desalination is returned to the ocean, maintaining the overall water-salt balance. The Mediterranean Sea has a negative water balance, where evaporation compensates for the inflow of neutral water, leading to a gradual increase in salinity. Furthermore, salinity varies throughout the Mediterranean, depending on depth and season, and the rate of seawater renewal varies from region to region, influenced by factors such as the input of rivers and adjacent waters, such as the Black Sea and the Atlantic Ocean. However, increased local salinity may negatively affect marine life. The problem is the amount of salt and the length of time spent in the brine. If the tide is greater than the surrounding seawater, the salt cloud can settle on the seafloor, affecting bottom-dwelling marine life rather than marine animal species.

3.4 Ecosystem Disruption

In addition to the large-scale impacts on global seawater quality, there are local environmental impacts observable in the coastal vegetation itself. Discharge areas around these facilities can become hotspots for saltwater accumulation, altering habitats unsuitable for many native species. These changes not only reduce local biodiversity but also promote invasive species capable of exploiting new conditions better than local ones, thus further destabilizing existing ecological relationships. This is an area that requires urgent attention from sustainability professionals worldwide. Mitigating some of the toxic effects associated with the highly saline wastewater released by coastal plants, as it rapidly dissolves in surrounding waters, affecting the delicate balances within oceanic environments. Potential solutions could include more efficient brine distribution techniques to mitigate the effects of brine and enhanced dilution to reduce direct damage from direct exposure. If space permits in arid areas, evaporation ponds could be used, allowing salt to be used/sold for industrial purposes.

Marine water quality is compromised by the improper disposal of brine from desalination processes.[13] Typically, for every liter of drinking water produced, approximately 1.5 liters of liquid contaminated with chlorine and copper are generated.

This toxic brine, when discharged into the ocean, can disrupt marine food chains, impair osmoregulation in marine organisms, deplete oxygen (anoxia) at the seabed, and impede photosynthesis in marine plants due to reduced light. Brine is often used as a source of water. Over long periods, this can lead to osmotic stress and the migration of marine species. Variations in salinity have different impacts on ecosystems, depending on species’ tolerance levels and their developmental stages.

3.5 Thermal Pollution Risks

All desalination processes, with the exception of reverse osmosis technology, involve thermal variations in feedwater transformations.

However, surface water temperature variations due to discharged brine are common to all desalination methods. Seasonal and various other factors can also cause feedwater temperatures to drop. Consequently, fouling of desalination membranes and other plant devices can increase due to higher ions released from the incoming water, requiring more extensive treatment, such as boron removal. These increased treatments can lead to pollution of shallow water ecosystems at brine discharge points due to high concentrations of antifoulant compounds. Indeed, variations in feedwater temperature are closely linked to the operation of desalination plants, and these two parameters can influence each other, potentially leading to increased pollution. Discharging brine onto shallow shorelines can cause local temperature changes near the outlet, which can have adverse effects on marine habitats. This is of particular concern regarding the impact of increased water temperature. It is therefore essential to understand the seasonal stratification of the sea.

3.6 Risks Associated with Total Alkalinity

The use of descalers in desalination processes can significantly alter brine alkalinity. Managing pH levels is essential to prevent precipitation on membranes and to maintain the bicarbonate-carbonate balance. Disruptions to this balance could lead to significant changes in discharge water alkalinity levels, potentially impacting marine ecosystems. Studies have shown that high brine alkalinity levels can have various effects on marine life, including altered physiological processes and habitat disruption. These effects are particularly pronounced in sensitive ecosystems such as coral reefs and seagrass beds, where high alkalinity can interfere with the calcification processes essential to their growth and survival. To mitigate these effects, process design must include a careful selection of antifouling additives. In some cases, it is advisable to pre-dilute brines before releasing them into the sea to reduce their impact on alkalinity. Careful management of chemical additives in desalination processes is therefore essential to minimize environmental risks.

4. Future solutions and funding avenues for desalination

Currently, while energy-intensive desalination systems that generate significant waste may be viable for wealthy nations facing water shortages, they do not represent an accessible solution for poorer countries facing water crises. Meanwhile, the scientific community is working to develop technological innovations aimed at solving both environmental and energy efficiency challenges.

• Carbon-free solutions are gradually becoming industrialized

The use of renewable energy sources for desalination is driven by technological advances, which are reducing the costs of photovoltaic power plants and reverse osmosis systems. At the same time, the instability surrounding fossil fuel prices and climate agreements is pushing toward the use of renewable energies. The trend is therefore largely favorable to the development of desalination plants powered by green energy, generally provided by solar panels, which take advantage of the abundant sunshine in water-stressed regions.

• Large-scale projects

Several projects to build large-capacity desalination plants linked to solar power plants are underway, particularly in the Middle East, which accounts for just under half of the world’s desalinated water production.

Seawater desalination, while offering a solution to freshwater scarcity, faces significant challenges, including its high cost. Therefore, funding sources play a crucial role in overcoming these obstacles and making desalination more accessible.

• Public financing with citizen participation

 Many desalination projects receive significant public funding (national or regional), but citizen participation can take the form of public consultations, debates on the social acceptability of the project, or contributions to funds dedicated to improving access to water. While this is not crowdfunding in the strict sense, it reflects a form of citizen involvement in the implicit financing of the project.

• Green bond financing

Infrastructure projects, potentially including desalination, can issue green bonds to attract private investment. These bonds are specifically dedicated to environmental projects and enjoy a positive image among investors concerned about the social and environmental impact of their investments. Although the investment is made by financial institutions, the approach is indirectly linked to the desire of citizens to invest in sustainable projects.

• Public-Private Partnerships (PPP)

PPPs are very common in large desalination projects. The private sector provides capital and technical expertise, while the public sector provides the regulatory framework and may contribute financially. Indirect citizen involvement occurs through taxes, which finance the public portion of the project.

Conclusion 

While it’s true that current desalination technologies are far from perfect, they can be made sustainable by focusing on a few critical criteria: Intake systems (systems that draw water from the oceans) should not negatively impact the local marine environment. Some factors to consider include lack of seabed erosion, low intake velocity, and location away from fish spawning areas. The discharge system (the system that pumps the wastewater—brine) should not impact the local marine environment. It should not discharge water at high temperatures and high velocities, introduce foreign particles or chemicals, or affect the flora and fauna of the local marine environment. The plant should operate at maximum efficiency. This includes the use of advanced centrifugal desalination pumps that operate with minimal energy consumption and maximum efficiency. The plant should have minimal to zero impact on the local environment during and after construction. The plant should use energy from renewable sources such as solar. With these criteria in place, it is possible to build sustainable desalination plants that address global water scarcity without harming the environment. With severe climate change and drought affecting the vast majority of the population, we believe desalination is the way forward. Combining renewable energy with improved technology can make desalination a sustainable solution in the coming years.

[1] https://www.sintechpumps.com.

[2] Food and Agriculture Organization, 2022.

[3] J. Herber, “The Price of Desalination: Factors and Solutions to Make Clean Water Affordable,” February 18, 2024.

[4] Ibid.

[5] Nick Ferris, “Can desalination save a drying world?,”Energy Monitor, January 17, 2023, https://www.energymonitor.ai/tech/can-desalination-save-a-drying-world/?cf-view.

[6] Jochen Bundschuh, Michał Kaczmarczyk, NoreddineGhaffour, and Barbara Tomaszewska “State-of-the-art of renewableenergy sources used in water desalination: Present and future prospects,” Desalination 208, (July 2021), https://www.sciencedirect.com/science/article/pii/S0011916421001065?via%3Dihub.

[7] A.G. (Tony) Fane, “A grand challenge for membrane desalination: More water, less carbon,”Desalination 426, (January 2018), https://www.sciencedirect.com/science/article/abs/pii/S0011916417320866?via%3Dihub.

[8] “Environmental Pollution,” https://www.env-news.com/environmental-pollution.

[9] Menachem Elimelech and William A. Phillip, “The Future of Seawater Desalination: Energy, Technology, and the Environment,” Science 333, no. 6043 (August 2011), https://www.science.org/doi/abs/10.1126/science.1200488.

[10] United Nations Environmental Programme 2008.

[11] Edward Jones, Manzoor Qadir, Michelle T.H. van Vliet, Vladimir Smakhtin, Seong-mu Kang, “The State of Desalination and Brine Production: A Global Outlook,” Science of the Total Environment657, (March 2019): pp. 1343-1356.

[12] Mustafa Omerspahic, Hareb Aljabri, Simil Siddiqui, and Imen Saadaoui, “Characteristics of Desalination Brine and Its Impacts on Marine chemistry and Health, With emphasis on the Arabian Gulf: A Review,” Frontiers in Marine Sciences 9 (2022).

[13] Yolanda Fernández Torquemada, José Miguel González-Correa, Angel Loya, and Luis Ferrero-Vicente, “Dispersion of brine discharge from seawater reverse osmosis desalination plants,” Desalination and Water Treatment 5(1-3): 137-145 (2009).; Perth Seawater Desalination Plant Water Quality Monitoring Programme. Rapport n° 445_001/3. Préparé par Oceanica Consulting Pty LTD pour la Water Corporation of Western Australia.