Rainwater and grey water: under what conditions is reuse permitted in France?
Over the last few months, French regulations have evolved around the reuse of rainwater and grey water for non-drinking, domestic and non-domestic purposes. The aim is to facilitate the recovery of "unconventional" water to reduce our costs and limit pressure on water resources.
Julie Mendret, University of Montpellier and Thomas Harmand, Aix-Marseille University (AMU)
Harvesting and using rainwater offers ecological and economic advantages: by collecting and using this natural resource, we reduce demand on drinking water networks, and preserve freshwater reserves.
This water is ideal for non-potable uses such as watering gardens, washing cars or flushing toilets, thus contributing to more sustainable management of water resources and reducing water-related costs for households and businesses.
Until very recently, the reuse of rainwater - water that falls directly from the sky in the form of precipitation - was governed in France by a decree dated August 21, 2008: this allowed it to be used, in particular, for excreta disposal, washing floors or watering green spaces, subject to certain conditions, notably relating to storage or signage. This legal framework has now beenamended to extend these uses.
A new legal framework
Non-domestic uses of rainwater are now authorized by the decree of August 29, 2023: for these uses, such as watering green spaces or cleaning vehicles, the rule is very simple: there are no restrictions.
The domestic use of rainwater, meanwhile, is regulated by a decree and an order dated July 12, 2024, which cover, more broadly, all water unfit for human consumption (EICH, a new name) for domestic use. These are distinct from water "intended for human consumption", known as potable water, and include: rainwater, freshwater, water from wells and boreholes for domestic use, grey water, and water from swimming pools for collective use - all of which are treated upstream.
Permitted uses include: washing clothes, washing indoor floors, disposing of excreta, supplying decorative fountains not intended for human consumption, cleaning outdoor surfaces (including vehicle washing if carried out at home), watering vegetable gardens and green spaces in buildings.
More flexible rules
The sanitary water quality levels required and the procedure to be followed depend on the type of water and its intended use. The text is fairly permissive when it comes to rainwater. All uses can be freely implemented after declaration to the town hall, with the exception of laundry, which must be declared to the prefect and comply with a certain quality level.
What's new in these two texts is the authorization to use EICH in "establishments open to the public" (ERPS). These include health establishments, spas and schools. In this context, the use of rainwater remains permitted, with free implementation (provided that the use has been declared to the town hall), with the exception once again of laundry and the supply of decorative fountains, which are subject to an additional declaration to be made to the prefect of the département in which the rainwater is used.
Rainwater used for these purposes must also meet the quality targets set by the aforementioned Order of July 12, 2024. This is not the case for rainwater used for purposes other than these.
Grey water reuse
These two texts also authorize the reuse of grey water (domestic wastewater from sinks, washbasins, showers, bathtubs and washing machines that does not contain faecal matter) and water from communal swimming pools.
The conditions are stricter here than for rainwater: the same uses can be envisaged, but with more constraints - none of which can be freely implemented with grey water or swimming pool water. The minimum procedure is a declaration to the prefect. Apart from ERPS, the following uses are authorized: supplying decorative fountains not intended for human consumption, excreta disposal, cleaning outdoor surfaces, and watering green spaces on a building scale.
These uses are possible subject to declaration to the prefect and compliance with minimum quality conditions. Laundry washing, indoor floor cleaning and watering vegetable gardens are subject to a derogation procedure, and may be authorized on an experimental basis. These experiments will be evaluated in 2035, and the decision to extend them will be taken accordingly.
Despite restrictions, commendable progress
For ERPS, the procedure is even stricter: authorization must be obtained to reuse grey water and/or swimming pool water to supply decorative fountains not intended for human consumption, to evacuate excreta, to clean exterior surfaces and to water green spaces throughout the building.
The procedures also differ in terms of monitoring requirements. For uses subject to quality requirements, monitoring is carried out to ensure that the water is harmless from a health point of view. For certain parameters, monitoring is required up to six times a year. As you can imagine, the cumbersome nature of these procedures will make it more difficult to implement this type of valorization in these establishments.
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However, it is important to emphasize the progress made possible by these texts: many unconventional water sources have now been identified and their use regulated, which is of major interest for the preservation of drinking water resources. By integrating these alternative sources into our water management, we reduce the pressure on freshwater reserves and limit the costs associated with the supply and treatment of drinking water. We will also contribute to more sustainable and resilient water management, particularly in times of drought or in regions where water is scarce.
Julie Mendret, Senior Lecturer, HDR, University of Montpellier and Thomas Harmand, PhD student in water law, Aix-Marseille University (AMU)
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