Is desalinated water the solution to water shortages in coastal areas?

Is desalinated water the solution to water shortages in coastal areas?

Is desalinated water the solution to water shortages in coastal areas?

Temps de lecture: 3

Desalination plants remove salt from salt water through a process called osmosis. The largest desalination plant in Europe is located in Torrevieja (Alicante), Spain, which produces 240,000 cubic meters of drinking water per day, or 80 cubic hectometers (hm3) per year. The complex, occupying 10 hectares, is located on the shores of Torrevieja’s famous pink lagoon and, paradoxically, next to the largest salt flats in Europe. In other words, the neighbors are in the opposite business: they evaporate the water and keep the salt for themselves. 

The Torrevieja desalination plant, managed by the state-owned company Acuamed, under the Ministry for Ecological Transition, was the largest in the world when it was built. It cost 226 million euros, was opened in 2014 with 40 hm3 of production per year and from 2019 doubled its capacity to the current 80 hm3. Ninety percent is used for irrigation and the rest for human supply. 

Currently, desalination is the solution that the Government offers to the Levantine irrigators, who are already partly fed with desalinated water, to overcome the decrease in the water they will receive from the Tagus-Segura water transfer. The Hydrological Plan of the Tagus Basin 2022-27 will focus on the ecological flows of the river and will cut 105 hm3 of water per year from 2027. The Minister for Ecological Transition, Teresa Ribera, has often announced the expansion of the production of the Torrevieja desalination plant from 80 hm3 to 120 hm3 to make up for the deficit of irrigators, without specifying when the increase will occur. 

The osmosis plant is the key to how desalination is produced and why neither experts nor irrigators see it as a clear alternative to water transfer. The high energy consumption that the process entails results into a much higher water price than that of the water transfer. The desalination plant consumes 51,000 kW/hour.  

« No, no, no », Lucas Jiménez, president of the Scrats union, which groups 80,000 irrigators, answers firmly when he is asked if desalination is the solution to the reduction of the water transfer. « The Segura basin plan drawn up by the Ministry itself says that desalination is not enough. Even if production is increased by 40 hm3 more, it does not repair the 105 hm3 lost. And, besides, the cost is unaffordable. When the Royal Decree-Law on drought was approved [March 2022] it was at 1.20 euros per cubic meters (m3). That is unaffordable for agriculture ». Desalinated water, Jiménez explains, is subsidized, so that of that 1.20 euros they pay about 0.53 cents per liter « depending on the fixed costs of each irrigation community ». The water from the inter-basin transfer Tajo-Segura costs them 0.30 cents. 

« The flows from desalination are complementary but never substitutes for water from the aqueduct for economic and environmental reasons, » says Joaquín Melgarejo, director of the Water Institute of the University of Alicante, who points out that water from the desalination plant costs « five times more ». « But there are also the environmental costs, which are less talked about. To produce one cubic meter of desalinated water in Torrevieja requires 3.8 kW, while the water from the aqueduct consumes 1 kW per m3. It depends on how this energy is produced, it will have more or less CO2 emissions. We are surprised that the Ministry intends to replace a water of 1 kW by one for which you need 3.8 kW in plant, » he adds. 

To reduce the cost of desalinated water, the plants would have to operate with renewable energy, such as photovoltaic energy. Montano, García-López et al. (2021) quantifie how much it would cost to expand desalination plants, install photovoltaic infrastructures in them and interconnect the desalination plants, as the Government intends. « In global terms it would be around 1,000 million euros that the State could spend on other activities if it did not touch the water transfer, if it maintained the ecological flows now established, » says Melgarejo. 

To convert the desalination plant to photovoltaic would require a huge area of solar panels, says the report, equivalent to the surface of the two lagoons in Torrevieja. « And the cost of water would not be reduced beyond 10-15%, it must be taken into account that the photovoltaic works for eight hours in the best case, » says Melgarejo. 

Espinosa-Tasón, Berbel et al. (2020) describe the evolution of the Spanish irrigated sector and focuses on water consumption, and energy use in the period 1950–2017. The analysis shows evidence of the basins reaching closure state and the impact on energy use from irrigation supply. The effect of this policy implies an increase in energy use by a factor of six in the period while the irrigated area triples and its water use doubles in the same period. The impact on energy consumption illustrates the water-energy nexus in Spanish agriculture and the change in the water policy paradigm. This paradigm shift implies an increase in production costs that is not always easily embraced by consumers (farmers and non-farmers alike). 


Based on “En la desaladora más grande de Europa, última estación del trasvase Tajo-Segura: « El agua desalada cuesta cinco veces más » El Mundo (7/11/2022) 

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