2015-04-29 08:54:54
In a context of sustainable development, the reuse of gray water in the domestic environment is often mentioned in order to save water resources and reduce drinking water consumption. In recent years, interest in this practice has grown and some countries such as Australia, the United States, Israel and Japan have turned to these additional resources when faced with situations of freshwater shortages.
In 2011, ANSES received a request from the Directorate General for Health to assess the health risks associated with the reuse of gray water for domestic purposes, a practice which is not currently authorized in France. The opinion and expert report published today define microbiological and physico-chemical quality criteria for treated gray water for certain domestic uses and recommend preventive measures to be implemented.
Health risks related to the different uses of gray water: each project is a special case
Raw gray water (or gray water) is water from showers, bathtubs, sinks, washing machines, sinks and dishwashers. The work carried out by ANSES’s experts shows that, to date, the data available is insufficient to rigorously and exhaustively characterize the dangers associated with the various physico-chemical and microbiological contaminants in gray water, and the levels of exposure related to different uses, applicable to all situations.
Gray water contains particulate and organic matter, and is contaminated by micro-organisms including pathogens and physico-chemical contaminants resulting in particular from hand washing, personal hygiene and cosmetic products, cleaning products from the house, washing surfaces and washing clothes. Given their characteristics, raw gray water cannot be reused for domestic purposes without prior treatment. Thus, the reuse of gray water requires treatment, transport and storage stages to be mastered.
Furthermore, the use of treated gray water in the home requires the installation of a separate network from the distribution network for water intended for human consumption (EDCH) and feedback from experience highlights the fact that the presence of a non-potable water network inside the home constitutes a major source of risk. In fact, the interconnection between the EDCH network and that conveying gray water, can lead to contamination of the EDCH public distribution network, making it non-compliant with the regulations in force and likely to have effects on consumer health.
The Agency’s recommendations
ANSES considers that the reuse of gray water in housing should only be considered for strictly limited uses, in geographical environments permanently and repeatedly affected by water shortages.
Subject to the implementation of treatment and appropriate risk management measures, treated gray water can be adapted to three uses in the domestic environment, if it meets specific quality criteria at the point of use:
- toilet flush supply;
- watering of green spaces (excluding vegetable gardens and agricultural uses);
- washing of exterior surfaces without generating aerosols (without using a high-pressure cleaner). However, in this case the addition of maintenance products to the treated gray water is not recommended.
Under these conditions, a regulatory framework for the conditions of collection, storage and treatment of raw gray water is necessary to reduce the health risks for exposed people.
In view of the lack of data needed to conduct an assessment of the health risks associated with the different uses of treated greywater, ANSES recommends that each project to reuse raw greywater in housing be subject to a systematic approach. risk analysis, to ensure that the benefits outweigh the risks to the health of the occupants and workers required to use treated gray water in the home.
The Agency recommends that decision-makers, individuals, co-owners, elected officials, etc. are informed of the possible health, environmental and economic impacts of the gray water reuse operation.
In addition, the addition of a gray water network can also create health risks for users and/or building occupants, whether related to the installation, operation and maintenance. of the network, or linked to the quality of the water transported. Traceability is therefore essential to guarantee food safety over time and avoid any drift.
In addition, the population (residents, professionals, occasional users) must be informed of the existence of a system for reusing treated gray water and of the possible health risks. They must also be trained in the conditions of use necessary to minimize the risks associated with the presence of a non-potable water network. ANSES also offers a series of practical recommendations for professionals working on greywater reuse facilities.
In a context of sustainable development aimed in particular at saving resources and saving water, the Agency reiterates that water, whatever its uses, must be used in a reasoned way.
Other Agency work
ANSES has already produced several opinions concerning the reuse of treated wastewater.
In addition, it was recently seized of a request for expertise relating to the reuse of rainwater.
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