U.S.-Mexican Water Sharing: Background and Recent Developments [Updated March 2, 2017] [open pdf - 2MB]
From the Summary: "The United States and Mexico share the waters of the Colorado River and Rio Grande pursuant to binational agreements. Increasing water demands and reduced supplies deriving from drought and air temperatures increase the challenges and significance of reliable water sharing. The International Boundary and Water Commission (IBWC) is charged with addressing issues that arise during application of binational water treaties. The IBWC is a binational entity with a U.S. Section that operates under foreign policy guidance from the U.S. Department of State. Under the binational 1944 Water Treaty, disputes and new developments can be resolved through agreed-upon interpretations of the treaty, called 'minutes'."
CRS Report for Congress, R43312
Congressional Research Service: https://crsreports.congress.gov/