Mexico and the United States each have a right to one-half of the Rio Grande main channel flow. Mexico has a right to two-thirds of the flows from the Rio Grande's Conchos, San Diego, San Rodrigo, Escondido, and Salado Rivers and the Las Vacas Arroyo tributaries (Mexican Tributaries).

The Rio Grande does not "belong" to any single entity; it is a transboundary water resource shared between the United States and Mexico, governed by complex international treaties and interstate compacts. Under the 1944 Water Treaty, the International Boundary and Water Commission (IBWC) manages the river's flow and distribution between the two nations. Internally in the U.S., the river's waters are further divided among Colorado, New Mexico, and Texas via the Rio Grande Compact of 1929. Legal disputes over "ownership" of the water continue into 2026, with the U.S. Supreme Court frequently intervening in cases where states or the federal government claim their rights have been violated. Effectively, the river is a shared legal responsibility where the federal government maintains "sovereign interests" related to international treaties, while states hold specific "usufructuary" rights to the water's use.