"How to share water has long been a complex issue for the U.S.-Mexico border region and in the broader U.S.-Mexico relationship. The two countries share a nearly 2,000-mile border. Multiple rivers cross the border or form the border at various points. The principal shared river basins are:  the Colorado River, which is predominantly in the United States, and crosses the Mexican border on its way to the Gulf of California (Figure 1), and  the Rio Grande, with major tributaries in the United States and Mexico and whose riverbed is the U.S.-Mexico border in Texas (Figure 2). […] This report is a primer on U.S. and Mexican water-sharing topics. It focuses on surface water quantity sharing and recent developments, including drought conditions. Due to Mexico's recent below-target deliveries of Rio Grande water to the United States, particular attention is given to the status, underlying causes, and responses to the Rio Grande water debt. This report describes:  legal obligations and processes under the 1944 Water Treaty;  drought conditions from 2010 to 2013;  water sharing and developments in the Colorado River Basin;  water sharing in the Rio Grande Basin and Mexico's water debt; and  stakeholder, diplomatic, and legislative responses to Mexico's Rio Grande water debt."
CRS Report for Congress, R43312