Since the beginning of the 20th century, the Carboniferous aquifer was known as a high potential aquifer. Groundwater has been exploited for decades to provide drinkable water and supply heavy factories in north of France and Belgium. Over-pumped during the last century, the Carboniferous aquifer has seen its water level dramatically decreased. Since the end of industrial period, groundwater consumption has decreased and water table is now stabilized and slowly coming back to a more “natural” level in some areas. However, this recent water level rise has triggered some chemical problems, such as the increase of sulphurs. The “Carboniferous limestones aquifer” is composed by two rock layers: the Visean and the Tournaisian, representing the lower parts of the Carboniferous era. The higher part of the aquifer is very productive and generally considered as a karstified zone. Recharge areas are located on the eastern part of the aquifer, in Belgium, where limestones laid under a few meters thick soil. Slightly dipping toward south - west, the geometry of the aquifer is not accurately known due to a lot of east - west faults and the presence of a faulted synclinal near Tournai (Be). In the past, a lot of hypotheses have been made regarding geometry and piezometry of this aquifer. Thanks to the “Scaldwin” project (launched in 2009), the assumptions are going to be set against more recent hydrogeological data and information provided by new borehole logs. In one hand, this project should encourage and stimulate international cooperation at large scale: studies and methods standardisation, data transfer and sharing, common reporting process. On the other hand, this cooperation will reduce scientific uncertainties about the Carboniferous aquifer: more accurate geometry, building of hydrogeological referentials, extension of piezometrical maps, hydrochemical and isotopic characterization of different groundwaters… New data from next field campaigns should help to generate a conceptual model of the aquifer behaviour, build a numerical model, and eventually modelize transfer functions between surface water and groundwater, in order to organize a sustainable management of the Carboniferous aquifer between France and Belgium.