To cope with droughts, France turns to wastewater

“We have to find other resources, it’s not normal that we only use drinking water to water green spaces or supply our toilets!” […]. We have had a culture of abundance, we have not adopted the habits of southern countries on this subject: less than 1% of treated wastewater is, in fact, reused. It’s ten times more in Italy, twenty times more in Spain, a hundred times more in Israel! It has almost become a refrain for the Minister of Ecological Transition Christophe Béchu: while droughts are set to increase with global warming, France must no longer lag behind in terms of wastewater reuse (“réut”, in the jargon of professionals), he insists. THE large “plan of water” which he is to announce at the end of March will include measures in this direction.

Administrative obstacles

If the “reut” rate is only 0.6% in France , against 8% in Italy, 14% in Spain, or 90% in Israel, it is because local authorities have not really needed it so far. Today, treated wastewater is mainly discharged into nature. Even if their reuse is governed by fairly strict health regulations (which will be reinforced from June 2023 by a European regulation of 2020), it is nonetheless possible.

“For the past fifteen years, authorizations have been granted within the framework of five-year experiments,” explains Régis Taisne, water specialist at the National Federation of Concessioning and Regulated Communities (FNCCR). Until then reserved for irrigation, these experiments were opened up to new uses by a decree of March 2022. “The administrative procedures remain long and complex, and the duration of the experiments too short”, continues the expert who hopes that the “water plan” will alleviate these administrative obstacles.

The economic equation of these projects can also be a major obstacle. “We have to apply an additional layer of treatment to the wastewater coming out of the treatment plants, then transport it to its place of use,” says Régis Taisne. An additional cost which constitutes a major blocking factor. »

The “reut” is profitable if it replaces drinking water. On the Ile de Ré, for example, potato producers have been using it for about ten years. “It had become impossible to pump groundwater, because new boreholes risked causing saline water intrusions,” explains Christophe Tanguy, director of strategic projects at SAUR. The producers had to use drinking water from the Continent: with the ‘réut’, we have divided the price of water by three! »

Discharges sometimes necessary

The economic equation is more complex for farmers who take their water from the natural environment. “Between the taxes, the energy used for pumping and the depreciation of the equipment, the water comes back to them between 5 to 7 cents per m3, against 30 to 50 cents per cubic meter within the framework of the ‘réut’”, says Régis Taisne.

However, the “reut” is not a miracle solution. The water discharged by treatment plants is also essential for supplying watercourses and enabling downstream uses. “Without the discharges from the Reims wastewater treatment plant, the Vesle, a small river that flows into the Aisne, would no longer flow in summer. Similarly, those of the Achères station, in the Yvelines, represent half of the low water flow of the Seine in summer”, notes Régis Taisne, acknowledging that “by the sea, the question arises less”.

Each “reus” project therefore requires in-depth studies, depending on the territory and the planned use. “We must also take into account the cost of a potential shortage,” underlines Christophe Tanguy. THE 117 municipalities having had to supply drinking water by tanker last summer will not say otherwise.

“By simplifying the procedures and systematically studying the feasibility of the “reut”, we could increase the rate from 1% to 10% in five years”, estimates Maxime Pellegrini, president of the Professional Federation of Water Companies ( FP2E). “This would correspond to 500 million m3, or 15% to 20% of the needs of the agricultural world”.

This would not exempt France from an effort of sobriety, while water will become increasingly scarce with global warming. “The ‘réut’ is only one lever among others to preserve the resource, with sobriety or the fight against leaks”, insists Christophe Tanguy. So many points which should also be the subject of measures in the government’s next “water plan”.