The reality of climate change is increasingly asserting itself regularly and more forcefully. Extreme phenomena, especially droughts, are expected to become more frequent, and the scarcity of water resources requires a rethinking of their usage within a framework of frugality.
The use of unconventional water sources (UWS), the definition of which remains to be clarified, can, within a territorially and integrated management framework, be an interesting solution to optimize the availability of water resources.
The potential of these unconventional water sources is currently insufficiently documented, but it is likely significant and still underutilized. However, while there is potential for improvement, especially compared to other countries that have been dealing with high water stress for a longer time, the investigation conducted by the mission shows that France has initiated a comparable number of projects to its Italian and Spanish neighbors, often highlighted.
The Action Plan for Resilient and Collaborative Water Management (Water Plan), launched by the President of the Republic on March 30, 2023, expresses a willingness to "massify" the use of these waters, with a target of developing 1,000 reuse projects in the territory by 2027.
This ambitious goal does not seem out of reach. The mission has inventoried 419 treated wastewater reuse (TWR) projects across the entire national territory ; among them, 136 projects are in operation. In addition, about thirty projects (non-exhaustive data) involving other unconventional water sources have been identified, representing significant volumes. A dynamic is therefore at work, which can be supported and amplified.
However, unconventional water sources are not a magical solution to the ongoing water scarcity issues and must find their rightful place among the bouquet of adaptation solutions to climate change. Regarding TWR, in particular, the mission emphasizes several points of vigilance that should guide the reflection on projects and the resulting instructions :
- TWR must be integrated with a prerequisite for controlling water consumption and frugality in usage, and must also be part of an overall territorial water management strategy aimed at reducing the vulnerability of the resource to climate change.
- TWR is economically and environmentally costly because it requires energy and chemical additives. It is neither new nor free water. Its mobilization must respond to a territorial need to avoid a supply-oriented policy disconnected from the needs and must be taken into account in the overall water withdrawal economy.
- While TWR appears generally as a "no-regret" solution in coastal areas, its implications for the receiving environment must be examined inland. The discharge from wastewater treatment plants can also significantly contribute to supporting low water levels in rivers.
- When a sanitation system does not comply with the "urban wastewater" directive, TWR must be excluded.
- Not all territories and contexts are suitable for TWR, and some uses may be more suitable than others based on a cost/benefit/risk analysis. In particular, urban uses by local authorities such as sewer network cleaning, washing bins, and service vehicles for cleanliness appear particularly suitable. Several experiments related to TWR for street cleaning and watering green spaces have recently been authorized, providing additional data on the relevance of water/use/employment triplets. The mission has also identified unconventional water sources that should be more valued, especially swimming pool water, drainage water, and geothermal water.
To expedite the implementation of projects, whose number has seen a significant increase since the drought of 2022, the mission suggests, in particular :
- Facilitating the Work of Services : Provide services with instructions, especially those related to health, to handle promptly requests not covered by current regulations. Ensure not to leave any use "orphaned," based on the capitalization of ongoing experiments, updating opinions from the National Agency for Food, Environmental and Occupational Health Safety (ANSES), and proposals from the High Council of Public Health (HCSP).
- Transition to a Declaration Regime : Shift to a declaration regime for the reuse of wastewater for sewer cleaning and cleaning of bins and service vehicles for cleanliness. After ongoing experiments, consider extending this regime to other urban uses such as street cleaning and watering green spaces.
The mission suggests, to enhance social acceptance of projects and minimize conflicts over uses, involving users early on and providing them with high-quality information on water resources and related challenges.
In terms of governance, the proposal is to establish a project director at the central level, as suggested by the Water Plan, and, at the local level, leverage the existing organization. This involves expanding the responsibilities of the interdepartmental mission for water and nature (MISEN) to a coordinating role on non-conventional waters (ENC), in connection with the regional level via the regional administrative committee (CAR).
The ongoing project inventory work undertaken by the mission could be effectively utilized to deploy the observatory for treated wastewater reuse (TWR) and expand it to cover non-conventional waters (UWS), in line with the objectives outlined in the Water Plan.
Lastly, the question of the role of non-conventional waters (UWS) in the overall water economy deserves consideration, ensuring that the ecological and financial effort is shared among all users.
