Rainwater and graywater: Under what conditions is it permitted to reuse them in France?
French regulations have evolved in recent months regarding the reuse of rainwater and graywater for non-potable, domestic, and non-domestic purposes. The goal is to facilitate the reuse of “non-conventional” water to reduce costs and limit pressure on water resources.
Julie Mendret, University of Montpellier and Thomas Harmand, Aix-Marseille University (AMU)
Rainwater harvesting and use offer both environmental and economic benefits: by collecting and using this natural resource, we reduce the demand on drinking water systems and thereby help 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 lower water 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 permitted its use, particularly for the disposal of human waste, 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 under the decree of August 29, 2023: for such uses—which include, for example, watering green spaces or washing 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, more broadly, apply to all water unfit for human consumption (referred to as EICH, a new designation) for domestic use. This category 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, graywater, and water from public swimming pools—all of which are treated prior to use.
Permitted uses include, among others: washing laundry, cleaning indoor floors, disposing of human waste, filling decorative fountains not intended for human consumption, cleaning outdoor surfaces (including washing vehicles if done at home), and watering vegetable gardens and green spaces on a building-by-building basis.
More Flexible Rules
Thus, the required water quality standards and the procedure to be followed depend on the type of water and its intended use. The law is fairly lenient with regard to rainwater. All uses are permitted after filing a declaration with the town hall, with the exception of laundry, which requires an additional declaration to the prefect and must meet a certain quality standard.
Another new feature of these two documents is the authorization to use EICH in “facilities serving vulnerable members of the public” (ERPS). This applies in particular to healthcare facilities, spa facilities, and schools. In this context, the use of rainwater remains permitted and may be implemented freely (provided that the use has been reported to city hall), with the exception—once again—of laundry and the operation of decorative fountains, which are subject to an additional declaration to be filed with the prefect of the department in which the rainwater is used.
Rainwater used for these purposes must also meet the quality standards set forth 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 documents also authorize the reuse of graywater (domestic wastewater from sinks, washbasins, showers, bathtubs, and washing machines that does not contain fecal matter) and water from public swimming pools.
The requirements here are stricter than those for rainwater: the same uses may be considered, but with more restrictions—none of them can be freely implemented with graywater or pool water. The minimum required procedure is to file a declaration with the prefect. Outside of ERPS, the following uses are authorized: supplying decorative fountains not intended for human consumption, flushing toilets, cleaning outdoor surfaces, and watering green spaces on a building-wide basis.
These uses are permitted provided they are reported to the prefect and meet minimum quality standards. The uses of washing laundry, cleaning indoor floors, and watering vegetable gardens are subject to an exemption procedure and may be authorized on an experimental basis. These experiments will be evaluated in 2035, and a decision on whether to implement them on a broader scale will be made accordingly.
Despite the restrictions, commendable progress
For ERPS, the procedure is even stricter: authorization must be obtained to reuse graywater and/or pool water for the following purposes: supplying decorative fountains not intended for human consumption, flushing toilets, cleaning outdoor surfaces, and watering green spaces on a building-wide basis.
The procedures also differ in terms of monitoring requirements. For uses subject to quality requirements, monitoring is implemented to ensure the safety of this water from a public health perspective. For certain parameters, this monitoring must be conducted up to six times a year: as one might expect given the complexity of these procedures, it will be more difficult to implement this type of water reuse in these facilities.
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It is important to note, however, the progress these regulations have enabled: 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 incorporating these alternative sources into our water management, we reduce pressure on freshwater reserves and limit 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, Associate Professor, HDR, University of Montpellier and Thomas Harmand, Ph.D. candidate in water law, Aix-Marseille University (AMU)
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