The Orange-Senqu is an internationally significant river system, located in the territories of Lesotho, South Africa, Botswana and Namibia. These countries rely to varying degrees on the river as a source of water for industry (mining and manufacturing), agriculture, energy, tourism, conservation and residential uses. The basin is degraded environmentally and continues to be threatened by anthropogenic factors. The Orange-Senqu river is important to regional cooperation as it crosses and forms some of the borders between the riparian states (figure 1) and provides the single largest water resource south of the Zambezi in a region which is classified as semi-arid and subject to increasing water stress. The highlands of Lesotho provide the only exception where the climate is temperate and annual rainfall exceeds evaporation. Elsewhere annual evaporative losses far exceed annual rainfall and to such a degree in the Lower Orange that the climate is classified as arid to hyper-arid. Certain areas of the Basin are already densely populated, economic development is significant, and socio-economic expectations are high. This causes an inevitable high degree of competition for the finite water resources that are available.