The European Water Framework Directive enjoins its members to retrieve the good ecological status of their water resources. In France, it has resulted in the regulation of entrants’ reduction plans which aim at halving the quantities of pesticides. This plan matches standard situations of non-point pollution sources, where the water infiltrates towards the underlying aquifer. However, numerous situations exist in France in which groundwater is imperfectly protected by a shallow impervious layer in the topsoil, meaning that sinkholes may connect the surface water and relay pollution directly to the aquifer. These impervious layers induce subsurface drainage demand and construction so that the effluent can be collected at outfalls of drainage systems, and be processed in constructed wetlands before falling down the sinkholes, thus decreasing net pollution. The Champigny aquifer corresponds to this description, and has been shown to be highly vulnerable. The mission of AQUI’Brie, a non-profit organisation, is to protect this groundwater, which is one of the water resources of Paris. Although well aware of the benefits of buffer zones, but at this time without incentives to implement them, AQUI’Brie started a co-construction process of constructed wetlands, involving all the stakeholders of a small catchment located upstream from a sinkhole. This paper describes the co-construction from the first meeting to the final structures in a context of high land use pressure. It shows that the number and area of constructed wetlands has diminished beyond the threshold for which the performance of depollution process may fail. In 2011, a performance assessment programme was set up to determine if the co-constructed wetlands comply with the new current regulations.