Irrigation with treated wastewater proposed in France

Irrigating with treated wastewater is gaining attention in France as a potential solution to water scarcity, especially during increasingly severe summer droughts. The government plans to increase the use of treated wastewater for irrigation, street cleaning, and watering green spaces and golf courses to 10% by 2030, up from 1% currently, as outlined in the Water Plan 2023.

Environmental risks of reduced river flow

This practice, however, may reduce river flows, which can constitute the total flow of rivers during the summer. This could negatively impact aquatic ecosystems, which depend on consistent water levels and quality. Scientists warn that this reduction might threaten aquatic animals and species reliant on river habitats.

Case-by-case evaluation of Reut projects

Water agencies, such as the Rhône Méditerranée Corse water agency, stress the need to assess Reut (reused water) projects individually. They ensure that water from wastewater treatment plants contributes to maintaining the base flow of rivers. Cerema, a public institution focused on adapting to climate change, is tasked with accelerating Reut projects while evaluating their environmental impact.

Challenges in water use legislation

Anthropologist Anne-Laure Collard highlights that the "win-win" argument for Reut overlooks growing tensions over water needs, especially for irrigation. She notes the difficulty of creating legislation that would prevent existing water withdrawals by farmers, even if it means accessing wastewater. Virginie Fouilliart from Cerema acknowledges that treated water could become a new resource withdrawn without being returned to the environment, potentially increasing environmental pressure.

Reut projects in regions with intermittent rivers

Ecologist Magali Gerino from the University of Toulouse points out that Reut questions are especially relevant in Occitanie, where most rivers are intermittent. She cites the Milhaud (Gard) project, where a new treatment unit was built to maintain river flow necessary for the survival of the protected Cistudo turtle species. This involved relocating an outdated wastewater plant and using part of the treated water with a filtration system to sustain river levels.

Limitations of wastewater for irrigation

Despite these efforts, treated wastewater is not a complete solution, as rivers are already heavily impacted by human activity and pollution, including discharges from wastewater treatment plants. For Reut, the water must be treated again, as even though wastewater discharged into rivers can benefit from dilution, it is unsuitable for direct use, especially for agriculture, which requires high-level treatment to ensure safety.

Regulatory changes and ongoing debates

Hélène Michaud from the Water Agency notes that agricultural projects are still highly regulated in terms of water quality, although regulations have evolved to support the development of Reut. Nassim Ait-Mouheb from the experimental wastewater reuse platform in Murviel-lès-Montpellier emphasizes that the debate on Reut shifts the focus from water quality to quantity, especially as water scarcity increases.

Reut’s role in crisis preparedness

Jérôme Harmand notes that Reut projects cause less debate for large rivers or coastal areas, where the volumes discharged are either minimal or into the sea. As water resources continue to decline in summer, Reut is seen as one of the strategies to prepare for crisis situations. However, the broader debate on Reut raises concerns about the future of rivers: whether they should be artificially maintained and polluted or allowed to dry in summer, especially as the number of intermittent rivers is expected to rise.