​On the international scene, USA area has undertook the first experience about the program exchange of credits in water quality mode can-and-trade in 2009. Now 32 States have established "trading programs" and/or "state policies" on the matter and no. 2 "inter-state trading  projects". Outside of the United States are currently reported N. 9 "trading programs", of which no. 1 in Europe (the Netherlands) and no. 3 "Comparative International Studies." CESI sustains the possibility to define a national program for water quality credit trading - between companies within the same river basin district - as a support to the quantitative  and quality objectives of water bodies provided for by the EU Directive 2000/60 (Water Framework Directive - WFD). The companies in the program can buy or sell credits of water quality within the limits - the cap - defined by the Plan refers to the district area (cap-and-trade). Units of water quality can be exchanged at national level between districts more and less virtuous one. Put a price on the shares of water quality, as experience taught in the trading of CO2, it could lead to a widespread commitment to the improvement of qualitative and quantitative characteristics of the resource and environmental systems connected to it. It is therefore necessary to define a path for the implementation of the program:Identification of an entity in charge of the management of environmental creditsIdentification of a set of quality parameters of the systemDefinition of units of entry: the person in charge of the program shall specify for each parameter included in the project, an entry in line with the global annual quality objectives. This assessment is expressed the severity of the operation environment.Creating a register of units of entryCreation of a system of self-control entriesAdoption of mechanisms to ensure that no violation of the lawIncentive   ​