Increased demand coupled with highly changeable availability – due primarily to the impacts of development and climate change – are increasingly impacting France’s water resource imbalance. In March 2023, the country launched an Action Plan for resilient and concerted Water Management (the Plan Eau) which highlighted among other things the potential from reuse of treated wastewater (Réutiliser les eaux usées traitées, or REUT). Two years on, where is its implementation up to?
Reducing pressure on water resources
Adopted pursuant to a 2020 European regulation due to come into force in June 2023, the Water Plan includes 53 measures aimed at optimising water usage efficiency, availability and quality while improving responses to episodes of drought.
Since then, plans for more efficient water usage have been drawn up across fifty industrial sites showing strong reduction potential. Roadmaps have been adopted for fifteen industrial sectors, and voluntary charters have been launched in the retail trade and among micro businesses. And, as of mid-April, the tourism sector is about to sign-up to three water efficiency plans (1) of its own.
Scale-up recovery of non-conventional water resources
Three key actions have been identified as part of a ‘Maximising Availability’ roadmap. This primarily aims to secure drinking water supply (in particular by leak reduction), increase recovery of non-conventional water resources (see box) and improve storage in soils, water tables and structures.
Definitions
According to Cerema (The French Centre for Studies on Risks, the Environment, Mobility and Urban Planning), non-conventional water resources (NCW) are types of water other than those derived directly from natural resources and that may be subject to appropriate treatment dependent on their usage. Reuse of treated wastewater, so the recovery of urban or industrial wastewater following its treatment in a wastewater treatment plant, therefore qualifies as one of these non-conventional water resources, as does rainwater* and grey water. Treated wastewater can be reused in a variety of ways: these include agricultural irrigation, watering green spaces, industrial consumption (process cooling, cleaning, etc) and urban or port activities including cleaning (jet cleaning of networks, road washing etc) and fire fighting.
*Rainwater is water from precipitation that is captured by a rain recovery system before it reaches the ground. This is distinct from stormwater which has reached and run-off the ground.
Less than 1% of the treated water volume in France
The reuse of treated wastewater is very marginal in France, representing less than 1% of treated water volumes. This compares to 14% in Spain, 87% in Israel and, eventually, 100% in Singapore. Japan and Italy lead the pack in reuse of treated wastewater for industrial waters, at 78% and 22% respectively.
Because less than 1% of the treated wastewater leaving treatment plants is reused, more than 99% is discharged to the natural environment – put simply, it is lost at sea. The French government hopes that the 2023 Water Plan will spearhead an increase to 10% by 2030, and to run 1000 projects for the reuse of non-conventional water across the country by 2027. Certain obstacles have now been removed through a number of decrees and ordinances, which simplified procedures, established a one-stop shop for applications at département level, and authorised certain usages in the agri-food industry, etc.
At the end of March 2025, 195 non-conventional water usage projects were operational or underway, among them 170 projects involving reuse of treated wastewater (of which 21 were operational at the end of 2024). Meanwhile, the acceleration programme for coastal reuse of treated wastewater, set up by Cerema and the French Association of Elected Coastal Officials (ANEL – Association nationale des élus du littoral), includes 33 communities that are or will be supported in developing strategy and conducting feasibility studies, in order to benefit from aid of up to 80% for the cost of these studies. This is financed by their providing Water Authority, the Banque des Territoires and the OFB (French Office for Biodiversity).
As indicated by Cerema, the reasons driving these communities to take action are varied: recovering water before it is lost to the sea; responding to pressures on this vital resource; optimising water use in areas facing high seasonal pressures; reducing, or even eliminating, discharge of treated wastewater into sensitive areas (bathing, shellfish farming, biodiversity), or to help prevent salt water contamination of water tables. The four main shared challenges are saving water, planning for droughts, preserving environments, and maintenance of economic activities.
Secondary treatment processes
The reuse of treated wastewater can employ several types of process to treat water exiting a wastewater treatment plant. Among these is lagooning (water treatment in several sequential basins) which permits microbiological parameters to be significantly reduced by natural processes and without needing energy, but which does require a large area. Activated sludge is another secondary treatment, but this frequently requires a further disinfection step (with a maturation lagoon). A further potential solution is the membrane bioreactor (MBR) which combines activated sludge and sludge separation using a membrane to purify the discharge. Some smaller communities employ biological processes as fixed culture (e.g. biofilters, biodiscs or reedbed filters) which they couple with a disinfection stage. Of 104 operational projects identified in France in 2022, 52% were activated sludge, 18% lagooning, 5% MBR, 4% biofilters or biodiscs and 1% reedbed filters, the rest (20%) remaining unknown(2).
Looking at industrial reuse of treated wastewater, numerous innovations are emerging. Examples include the mobile nanofiltration module offered by NSI and NX filtration, a system based on Exocell flotation, and Veolia’s linking together of several technologies (MBR, anaerobic treatment with granular biomass, and reverse osmosis). Not to be overlooked is the microalgae-based system developed by start-up Zeni, which simultaneously purifies industrial water, sequesters carbon and recovers algae primarily as biostimulants.
Will we see treated wastewater used in drinking water?
As outlined above, possible uses range from agricultural irrigation to urban uses, watering green spaces and supplying industrial processes. Reusing treated wastewater in drinking water is therefore off the table. Nonetheless, an indirect purification system is being tested in Sables-d’Olonne in western France as part of the Jourdain program led by Vendée Eau(3). Part of the treated water is recovered at the treatment plant’s outlet (150 m3/h from a total 600 m3 /h). This water is then treated again in a refining plant (ultrafiltration and low pressure reverse osmosis with membranes, UV disinfection and chlorination). It is then transported over 25 km to a dam, where it’s discharged into a green area and mixed with water from the river. A slow transit through the reservoir follows, finishing in the drinking water production plant where it is rendered suitable for drinking. This experiment, performed over a ten-year period, could be replicated in the future.
1) cf. tourist accommodation, sports sector and tourism sites, the idea being to “mobilise tourism professionals around more sustainable and resilient practices.” When these are signed on 26 April, the 25 winners of the call for expression of interest for Management of water resources in tourism will also be unveiled.
2) “Overview of the reuse of treated wastewater in France – State of play in 2022 and evolution since 2017 “, Epnac survey conducted by Inrae, July 2023.
3) It should be remembered that this part of western France (the Vendée) has surface sources (watercourses) that are subject to significant water stress in summer, an issue further accentuated by tourism demand.
Coming soon – a methodological guide to the Reuse of treated wastewater
A methodological guide on the reuse of treated wastewater is being produced by Ecofilae, commissioned by the collaborative association, Record. This should be published in the course of 2025. The development of this guide, which associates techno-economic criteria with environmental and health impact criteria, should allow industry and communities to promote these approaches, prioritise their actions and base their technological choices around the most suitable solutions.
