How can the reuse of treated wastewater be promoted in France?

Jérôme Harmand, Nassim Ait Mouheb, Sami Bouarfa, July 2025

The Conversation

To download : news-30744-reut-guide.pdf (17 MiB)

In France, the Water Plan announced by the President of the Republic in 2023 set a target of developing 1,000 projects for the reuse of ‘non-conventional water (ENC)’ by 2027. This is an intermediate target before aiming for 10% reuse of treated wastewater (REUT) by 2030.

If pursued without sufficient discernment, this national quantitative target could lead to maladaptation and inappropriate projects. For example, projects that would result in an increase in the overall amount of water consumed due to the ‘rebound effect’. The risk would be to present REUT as a new resource, even though this remobilised water is likely to be lacking in natural environments.

However, the state of the art in science and analysis of international experience confirm the value of water reuse in responding to situations of high stress. These same experiences also show that projects are strongly influenced by local constraints.

In other words, their success will depend on the involvement of stakeholders, the match between the required water quality and the level of treatment technology, the economic viability of projects, etc.

Wastewater: a resource rather than waste

To help our societies adapt to climate change and preserve our environment, controlled and responsible water management is essential, both in terms of quantity and quality. This is a strategic issue for ensuring sustainable living conditions for all.

This requires, in particular, the rationalisation and optimisation of water use and the sharing of resources. Above all, the state of aquatic environments must be taken into account. For example, the environmental role of treated wastewater in maintaining low water flows during periods of drought should be considered.

In this context, wastewater should no longer be considered as waste to be treated and disposed of, but as a resource. This water can, for example, be rich in fertilisers that are useful for agricultural crops. In a circular economy, it can be considered as a value stream, depending on specific local conditions (match between crop needs and available water, proximity of uses, etc.).

Domestic wastewater is the main resource that can be mobilised. However, the concept of the circular water economy needs to be extended to all non-conventional water. For example, rainwater, swimming pool water or water drained from underground to enable the operation of underground structures such as metros, tunnels or car parks. This makes it possible to balance usage and withdrawals as effectively as possible across a given territory.

Closing the ‘small’ and ‘large’ water cycles

To cope with pressure on resources, we need to come up with new approaches. The challenge is to rethink how we use water throughout the value chain. To do this, we can imagine circular uses (reuse after a previous use) where they have until now been linear (extraction, use, discharge).

This involves designing a more integrated water management system at the regional level, which will constrain resources and needs. The aim is to ensure that the usage cycle disrupts the ‘large’ (or natural) water cycle as little as possible, both quantitatively and qualitatively.

The agricultural, urban or industrial context is also important. It requires an examination of environmental and health risks. Indeed, it involves modifying the water cycle. The implementation of solutions that favour short cycles can impact environments and populations to varying degrees. This is particularly true in periods of severe drought.

For example, the microbiological quality of water can be an issue in situations of indirect reuse. In this case, the water is not taken directly at the outlet of the treatment plant (where it would then be subject to quality standards for reuse), but downstream, in the watercourse into which the treatment plant discharges. This type of abstraction is only regulated by quantitative constraints, and no longer by qualitative constraints.

Which projects are successful?

The state of the art in science and analysis of international feedback are useful for identifying the factors that make these projects successful.

Firstly, they benefit from a favourable geographical context. For example, when the distance between the sources and potential uses is reasonable or when hydraulic infrastructure already exists.

They also organise consultation between the various stakeholders involved (managers, farmers, consumers, financiers, etc.). The challenge is to involve them in governance in order to better align their respective interests.

They also put in place a health and environmental risk management plan, for example by adopting a multi-barrier approach.

These projects would benefit from a clear and harmonised regulatory and normative framework at a scale that goes beyond the national level in order to take advantage of international experience. With the exception of reuse for agricultural purposes, wastewater regulations could be improved to be better calibrated, more consistent, less complex and more sustainable.

Finally, these projects must mobilise economic models that strike a balance between the producing and beneficiary stakeholders. They should be based on a case-by-case analysis of the profitability of infrastructure, the financing and operation of which often involve both private and public actors.

Best practices to adopt

To promote the success of REUT projects, responsible water management must first be made a priority in every country around the world. This means enshrining the necessary environmental policy instruments in law, without making the current frameworks more cumbersome and complex.

It also requires the promotion of preliminary measures. These include water conservation, optimisation and on-site recycling during the design and operation of new infrastructure. To minimise human impact on the natural water cycle, it is better to reuse a cubic metre of wastewater than to extract it from the natural environment.

The project’s cost-benefit analysis should include its health, social and environmental impacts and benefits throughout its entire life cycle, as well as the overall opportunity cost.

The recycling of extracted water could also be incorporated into all water development and management master plans. REUT can thus be integrated into regional water management plans (PTGE) and water development and management plans (SAGE).

Only then can multi-resource and multi-use reuse of wastewater be designed and planned (where possible and relevant). This makes it possible to substitute REUT for other withdrawals from the environment or the use of drinking water. To this end, the challenges of restoring and preserving resources and ecosystems must be systematically taken into account

This also requires a rethinking of public service delegation tenders and contracts. The purpose and various functions of wastewater treatment plants should be taken into account, and their role as ‘treatment plants’ should be expanded to that of genuine recovery plants, where relevant.

Beyond water recovery, nutrients such as nitrogen and phosphorus can be extracted, and heat can be produced. However, for this to be possible, tax instruments, pricing methods and, more broadly, economic models need to be adapted accordingly.

Strengthening financial support for research on this issue is crucial. Examples at various levels include the Défi Clé Water Occitanie (WOc), the REUTOSUD project, the Water4All funding programme and the European research network Water4Reuse.

This also requires the creation and coordination of structures for awareness-raising, knowledge exchange and consultation. These must involve national, regional and local public authorities alongside other stakeholders. These interdisciplinary research-action schemes, known as ‘Living Labs’, are rooted in local areas and at the interface between science, politics and society. Like the Living Labs set up as part of the aforementioned WOc, they must facilitate the design of new tools, services and uses for water recycling.

Finally, it is important to promote acculturation throughout the technical and administrative chain. This requires initial and ongoing training for professionals, design offices, elected officials and central and local government officials. This will facilitate the implementation of these new water management approaches, in the interests of a circular water economy.

Sources

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