Is the desalination of sea water really a drinkable solution to shortages?

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Patrice Quilici checks the level of his drinking water tank every day, which is visibly dropping. The stock has already halved since August 1. “Despite maximum restrictions, there are only 8,000 m3 of water left”, worries the mayor of Rogliano, in Haute-Corse, Tuesday, August 9. In summer, the population of this tourist village of 650 inhabitants is multiplied by ten. Mechanically, water consumption increases. “Desalinating seawater is the only solution we have left, I have no choice”, explains the aedile. He hopes that his desalination unit will be commissioned on September 10.

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Where sea water is abundantly available and fresh water scarce, the emergency has pushed other municipalities to take this path. The island of Groix (Morbihan) was already on drought alert before summer, a season during which the population more than doubles. The municipality is equipped with a desalination plant, active since August 3.

The island of Sein (Finistère), isolated, has produced its own water thanks to a desalination plant since 1973. On the small Ile-Molène, off the coast of Finistère, the situation in terms of drinking water was deemed “worrying” before the installation of a unit this summer, which covers about 60% of daily needs. Without her, “we would have lasted two or three weeks in July and it was over”explained to TF1 the mayor, Didier Delhalle.

Significant drawbacks, however, qualify the relief: the cost of desalination weighs heavily on the budget of small municipalities. In Molène, the operation costs 65,000 euros for three months. In Groix, the desalination unit just installed represents a cost of 800,000 euros out of a budget of 7.5 million euros in 2021. “It’s a rather expensive technique”confirms Bernard Barraqué, specialist in water policy and researcher emeritus at the CNRS.

“The desalination plant is not very expensive in investment, but relatively expensive in operation.”

Bernard Barraqué, water policy specialist

at franceinfo

This cost is explained by the energy-intensive process of desalination. In Corsica, the price of the fuel necessary for the operation of the unit inflates the bill, which amounts to approximately 1.05 million euros. “We may have the most expensive water in France”, concedes Didier Fouquet, mayor of the island of Sein. There, the installation of a wind turbine next year aims to reduce the price of a cubic meter of water on the island, which amounts to 7.50 euros, while the French average hovers around 4 euros.

Specialists see another limit to these desalination techniques. The operation, which most often involves separating water molecules and salt through a membrane, produces waste. The latter are not safe for nature: for one liter of drinking water produced, 1.5 liters of brine, according to a UN report (in English) released in 2019. This salty, mineral-rich mud is usually dumped into the sea.

“Salt discharge can have effects on fauna and flora, which are not used to such high salt concentration levels.”

Nicolas Roche, researcher in environmental geosciences

at franceinfo

The Mediterranean is particularly threatened by these discharges. “The rejected brine is denser than sea water, it does not mix and sinks to the bottom“, explains Christophe Mori, freshwater specialist at the University of Corsica. “It affects the‘Posidonia seagrass, present on the entire Corsican coast, which is a place of shelter for the species. It is a plant very sensitive to salt, down to the milligram”, continues the professor.

Too few studies are carried out on the subject, according to him, but the consequences on these endemic underwater grasses of the Mediterranean have nevertheless been measured in Cyprus, near two of the largest desalination plants on the island. The data shows “repercussions on the marine environment near brine discharge points” with “a sharp reduction in shoot density and leaf area”.

Salt concentration is not the only hazard of these chemical-laden discharges from water treatment. The spilled brine is also warmer than sea water and risks aggravating the warming of the Mediterranean, whose temperature this year was 5°C higher than in other summers.

Unlike France, other countries have invested massively in real desalination plants, such as Singapore, the Maghreb countries, those of the Middle East or those of the Gulf. There, desalination is often the only source of fresh water for agriculture, industry and homes. In Jordan, a factory is to be set up on the shores of the Red Sea in 2026, after a billion dollars of work. She should produce “between 250 and 300 million m3 of drinking water per year”according to the authorities, or about 750 million liters of water per day.

Small projects are also on the rise. “In Tunisia or in certain Greek islands, large hotels are equipped with a small desalination unit to avoid the vagaries of possible malfunctioning of the public network”, evokes Bernard Barraqué. These choices bear witness to a selfish strategy and “a break in solidarity” with the population of these regions in the event of a lack of water. In France, metropolitan coastlines are currently very far from being colonized by desalination units. “Until now, we didn’t need it”explains the researcher.

Apart from the island of Sein, the three stations set up this year are only there to partially cover the water needs of a very small part of the population. And they must remain so, insists the government. “Desalination is more of an emergency solution, which is difficult to generalize at this stage”according to the Ministry of Ecological Transition.

These energy-intensive units contribute to global warming when they run on fossil fuels, as in Corsica. “Using a desalination unit is like turning on the air conditioningcompares Christophe Mori. We amplify climate change, so we increase the risk of drought.” For the specialist, “we are always in an action on the consequences and never on the causes”.

As the drought sets in, however, these desalination units could remain in place after an overheated summer of 2022. On Ile-Molène, the sustainability of the small resort is being studied, with new investments planned. “It will repeat itself, that’s why we bought this equipment”, confirms Patrice Quilici, the mayor of Rogliano. Unlike 2002, when the Corsican municipality got rid of its unit after a brief episode of water shortage, the municipality intends to use it for several years, before other solutions are put in place.

For Christophe Mori, if the use of a desalination unit seems necessary in the short term, other less polluting tracks could apply to Rogliano and Corsica. Starting with the development of hill reservoirs, small dams that can store water on the side of a river. According to experts, the water consumption pattern also needs to be reviewed, particularly in agriculture: “In Corsica, continuing to grow corn, which is very water-intensive, is heresy”believes Christophe Mori.

Repairing and optimizing the water distribution network could also save precious liquid. In France in 2020, around 20% of water is lost due to leaks in the network, estimates the Observatory of public water and sanitation services.

Reduce consumption, recycle wastewater… “We must put in place a virtuous system for the use of water”, insists the researcher Nicolas Roche. This is what Belle-Ile-en-Mer is trying to do. The Morbihan island has chosen the opposite path to Molène, Rogliano or Groix. Since 2015, it has been without the desalination unit installed at the end of the 2000s. The intermunicipal authority has opted for better rainwater collection, which allows it to supply its water reservoirs more easily. For municipalities where access to drinking water is a sensitive, even vital issue, desalination does not necessarily come naturally.


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