Romain Rouillard / Photo credit: JC MILHET / HANS LUCAS / HANS LUCAS VIA AFP 6:30 a.m., March 22, 2024
To preserve water resources in the face of episodes of drought likely to multiply in the territory, the hypothesis of reusing wastewater regularly resurfaces. On the occasion of International Water Day, focus on this process, relevant for certain uses, without being the miracle solution hoped for.
This is a department where he can almost no longer do so. In the Pyrénées-Orientales, less than 500 millimeters of water fell over the last two years while the expected annual average is, according to Météo France, around 570 millimeters. Placed in a “crisis” situation by the site vigieau.gouv.fr, the department is experiencing an increasingly desert climate and the management of water resources has become a major issue. Visiting the department this Thursday, on the eve of International Water Day, the Minister of Ecological Transition, Christophe Béchu, announced the implementation of projects to deal with this drought.
A lack of water which extends well beyond the Pyrénées-Orientales, during the summer period. This is evidenced by the spectacular episode of summer 2022 during which the rainfall deficit reached 85% in July, again according to Météo France.
More relevant in coastal areas
Among the solutions regularly mentioned to compensate for this lack of water is the reuse of wastewater. As part of the “Water Plan”, presented by Emmanuel Macron at the end of March 2023, a decree, published at the end of January, authorizes food manufacturers to reuse this water, provided they respect a strict framework. “These waters must have no influence, direct or indirect, on the safety of the final foodstuff and on the health of the consumer,” specifies the text, which provides for exclusions for certain waters having been in contact, for example, with certain animal products.
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Should we then accelerate this path of reuse? It all depends on the local context. “It is more relevant in coastal areas, because there, certain wastewater treatment plants discharge into the sea, which leads to a loss of fresh water,” indicates Julie Mendret, lecturer at the University of Montpellier and specialist in new urban wastewater treatment processes.
Elsewhere, this water is, most of the time, reinjected into waterways, after passing through the purification unit. Their reuse could therefore amount to undressing Peter to dress Paul. “This is water that will no longer go into the river to support the flow rates,” notes Vazken Andréassian, hydrologist and research director at Inrae. And added: “During the great drought of 2022, there are lots of places where the rivers, dry, started to flow again after the treatment plant”. Not to mention the damage caused to the maintenance of ecosystems.
No significant gains to hope for
Furthermore, points out the researcher, "this reuse will not create additional water. It's just water that we are redirecting." It is therefore difficult to see a magic solution to water shortages. “I wouldn't say it's of no interest because it's not true, but in terms of quantity, it won't be huge gains to hope for.”
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On the other hand, the reuse of this water proves very useful for agricultural purposes, thanks to the nutrients provided to crops, but also for various urban users, such as cleaning roads. It can also improve water quality for certain activities such as shellfish farming (the farming of edible shellfish).
Conversely
, the processes to transform this water into drinking water are much more tedious. "It's very marginal. There is only one project in France that does it, it's the Jourdain project. And again, they are not going to produce drinking water, they are going to reinject it into the water reservoir which serves as a reserve to go to the purification plant. This is what we call indirect purification. But technically, we have the capacity to do it, but it is something that will cost very expensive", explains Julie Mendret. For the experts interviewed, only sobriety prevails to sustainably preserve water resources.