Almost 50 countries have more than three-quarters of their land in international river basins; 214 river basins around the world are international in the sense that they are shared. While many resource scarcities tend to threaten internal stability, water shortages in some regions threaten international conflict.
The water scarcity problematique was illustrated at an early stage by the Segura Basin in Spain, where interbasin solidarity over water use and transfer became part of the cultural heritage from the 8th century - and has turned out to be difficult to abandon. Increasing consumption of groundwater has now reduced the volume of the Tagus River Water Transfer, so that the Tagus aqueduct carries only one third of the capacity.
Symptoms of water stress exist around the world -- not only just in water scarce countries, but in parts of water-wealthy ones as well.
In Rio Grande, shared between Mexico and USA, water scarcity was a hot issue that is causing large concern and special water management challenges, especially during the current drought when the river went empty in the downstream end. What is now primarily considered is an intersectoral water transfer from agriculture to industry.
In the Curu basin in Brazil the landscape was described as crowded with reservoirs for compensation of the high rainfall seasonality (Beekman). In view of the small-scale catchments in the region, the basin approach had been replaced by a multi-basin management approach.