The case study presented is focused on the use of tradable and rentable water permits designed to maximise the efficiency of the use of water resources in Colorado (USA). The State of Colorado is divided into two distinct regions: the eastern, dry plains and the western areas that start with the Rocky Mountains and extend through rugged lands to the western border of the State. Rainfall and snow are heavy on the western side of the Rockies, while the eastern slopes of the mountains (the "East Slope") and the plains are semi-arid. In order to compensate this unequal distribution of the water resources, a complicated project of water transfer has been designed. The Colorado-Big Thompson Project is the largest transmountain water diversion project in Colorado. Built between 1938 and 1957, the C-BT Project provides supplemental water to 30 cities and towns and is used to provide supplemental irrigation to 693,000 acres of north-eastern. In order to efficiently manage the "foreign water provision" ensured by the CB-t project, it was founded the Northern Colorado Water Conservation District (NCWCD). It was established in 1937 to contract with the Federal Government to build the large trans-mountain water transfer project. NCWCD is responsible for the diversion works of the project and for the allocation of water on the eastern side of the mountains.