Rainwater and gray water: under what conditions is it permitted to reuse them in France?
French regulations have evolved in recent months with regard to the reuse of rainwater and gray water for non-potable, domestic, and non-domestic purposes. The aim is to facilitate the recovery of "unconventional" water in order to reduce our costs and limit pressure on water resources.
Julie Mendret, University of Montpellier and Thomas Harmand, Aix-Marseille University (AMU)
The collection and use of rainwater offers both environmental and economic benefits: by collecting and using this natural resource, we reduce demand on drinking water networks and thus preserve freshwater reserves.
This water is ideal for non-potable uses such as watering gardens, washing cars, or flushing toilets, thereby contributing to more sustainable water resource management and reducing water-related costs for households and businesses.
Until very recently, the reuse of rainwater —which refers to water that falls directly from the sky in the form of precipitation—was regulated in France by a decree dated August 21, 2008: it allowed its use, in particular for the disposal of excreta, washing floors, or watering green spaces under certain conditions, notably related to storage and signage. This legal framework has justbeen updated to expand these uses.
A new legal framework
Non-domestic uses of rainwater are now authorized by the decree of August 29, 2023: for cases such as watering green spaces or cleaning vehicles, the rule is very simple: there are no restrictions.
Domestic uses of rainwater are regulated by a decree and order dated July 12, 2024, which more broadly covers all water unfit for human consumption (known as EICH, a new designation) for domestic use. This water is distinct from water "intended for human consumption, " known as potable water, and includes: rainwater, fresh water, water from wells and boreholes for domestic use, gray water, and water from public swimming pools—all of which is treated upstream.
Permitted uses include: washing laundry, washing indoor floors, disposing of excrement, feeding decorative fountains not intended for human consumption, cleaning outdoor surfaces (including washing vehicles if done at home), watering vegetable gardens and green spaces around buildings.
Relaxed rules
Thus, the required water quality standards and the procedure to be followed depend on the type of water and its intended use. The text is fairly permissive with regard to rainwater. All uses are permitted after declaration to the local council, with the exception of laundry, which must be declared separately to the prefect and must meet certain quality standards.
Another new feature of these two texts is the authorization to use EICHs in "establishments receiving sensitive members of the public" (ERPS). This applies in particular to healthcare establishments, spas, and schools. In this context, the use of rainwater remains permitted, with free implementation (provided that its use has been declared to the town hall), with the exception, once again, of laundry washing and the supply of decorative fountains, which are subject to an additional declaration to be made to the prefect of the department in which the rainwater is used.
Rainwater used for these purposes must also meet the quality standards set out in the aforementioned decree of July 12, 2024. This is not the case for rainwater used for purposes other than these.
Greywater reuse
These two texts also authorize the reuse of gray water (domestic wastewater from sinks, washbasins, showers, bathtubs, and washing machines that does not contain fecal matter) and water from public swimming pools.
The conditions are stricter than for rainwater: the same uses can be considered, but with more restrictions—none can be freely implemented with gray water or pool water. The minimum procedure applicable is notification to the prefect. Outside of ERPS, the following uses are authorized: feeding decorative fountains not intended for human consumption, disposal of excreta, cleaning of exterior surfaces, and watering of green spaces at the building level.
These uses are possible subject to notification to the prefect and compliance with minimum quality conditions. The uses of washing clothes, cleaning indoor floors, 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 a decision will be made on whether to generalize their use.
Despite restrictions, commendable progress
For ERPS, the procedure is even stricter: authorization must be obtained to reuse gray water and/or swimming pool water for decorative fountains not intended for human consumption, excreta disposal, cleaning of exterior surfaces, and watering of green spaces at the building level.
The procedures also differ in terms of monitoring requirements. For uses subject to quality requirements, monitoring is put in place to ensure that the water is safe from a health perspective. This must be carried out up to six times a year for certain parameters: given the complexity of these procedures, it will be more difficult to implement this type of recovery in these establishments.
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However, it is important to highlight the progress made possible by these texts: numerous unconventional water sources have now been identified and their use regulated, which is of major importance for the preservation of drinking water resources. By integrating these alternative sources into our water management, we are reducing pressure on freshwater reserves and limiting the costs associated with supplying and treating drinking water. We will also contribute to more sustainable and resilient water management, particularly during periods 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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