In France, unlike countries such as the USA, Australia and Israel, grey water cannot be reused. However, the government recently commissioned a study on the topic, which suggests it could be done under specific conditions:
- The water would have to have any contaminants removed and be channeled through a closed circuit to avoid contamination of the public water system.
- Grey water is not potable and would need to undergo filtration to eliminate synthetic and organic matter. A constructed wetland and membrane filtration are two possible avenues to explore.
Here is an article in French if you want to read more about it: http://www.consoglobe.com/recuperer-les-eaux-grises-oui-mais-prudence-previent-lanses-cg
All wastewater contains not only solid pollutants but diffuse ones as well. And no filter will be able to fully remove them. They will become dispersed throughout the constructed wetland and eventually make their way into waterways during periods of heavy rainfall.