Treaty relating to the utilization of waters of the Colorado and Tijuana Rivers and of the Rio Grande

The Treaty relating to the utilization of waters of the Colorado and Tijuana Rivers and of the Rio Grande (also known as Treaty on Utilization of Waters of the Colorado and Tijuana Rivers and of the Rio Grande or 1944 Water Treaty) is a cooperative water agreement between the United States of America and Mexico defining allocation of Rio Grande water to the U.S. and Colorado River water to Mexico. The agreement was signed in 1944 as an instrument of the International Boundary and Water Commission (IBWC). The agreement is a subject to frequent changes, delivered through the so-called "Minute Process".

The agreement worked well for 50 years as a tool for peaceful resolution of transborder water management issues, but since the end of the 20th century, Mexico's deliveries to the U.S. have at times come up short.

Agreement and the Commission
The agreement defined the composition of the IBWC, including its current name and professional character (both U.S. and Mexican heads are to be engineers). The Commission objectives were set as follows:
 * cross-border redistribution of water of the Colorado River and the Rio Grande,
 * joint U.S./Mexico efforts to regulate and conserve Rio Grande waters by constructing dams and reservoirs,
 * regulation of the Colorado River to preserve waters allocated to Mexico,
 * flood protection.

Provisions
The annual cross-border allocations were defined as follows:
 * 350,000 acre-feet from Mexico (Rio Grande) to the U.S.
 * 300,000 acre-feet from the U.S. (Colorado River) to Mexico.

Drought can be accommodated by lower deliveries that should be made up within the 5-year accounting "cycle" (the concept was updated via Minute 234 in 1969). A declaration of an "extraordinary drought" allows for rolling the 5-year debt into the next 5-year interval. The treaty did not define a procedure for such declaration and does not allow rolling the debt over to yet another 5-year period. Mexico's accumulated water debt is written off once the reservoirs behind Falcon and Amistad Dams become full, with this event starting a new 5-year cycle.

To expedite the negotiations on the primary issue (surface waters), the issue of groundwater was deliberately set aside.

Minute system
Article 25 of the treaty created a "minute system", a vehicle that allows rapid changes to accommodate water flow variations, environmental conditions, and technical accidents. Each "minute" is a result of negotiations performed by IBWC/CILA Commissioners. The minutes are considered to be interpretations of the treaty, not amendments to it, and therefore do not require action of legislatures to become active: each government has a 30-day window to object, without such an objection, a minute becomes a binding agreement between the countries. Due to the minute system the treaty is considered to be one of the most flexible binational agreements in the world.

Since 2022 the Rio Grande Minute Working Group consists of representatives from IBWC, Texas Commission on Environmental Quality, US Department of State, the Mexican arm of the IBWC (CILA), and the Mexican Comisión Nacional del Agua (CONAGUA).

Rio Grande allocations
Per the treaty, the countries have the following entitlements: A special provision ensures that the US $2/3$ share of the flow from the Mexican tributaries "shall not be less, as an average ... than 350 000 acre-feet annually".
 * Mexico:
 * all waters from the San Juan River and Rio Alamo;
 * half of Rio Grande's main channel flow below the southernmost international dam;
 * two-thirds of flows into the main channel from Rio Conchos, Arroyo de las Vacas, Rio San Diego, Rio San Rodrigo, Rio Escondido, Rio Salado;
 * half of all other main channel flow not mentioned above.
 * US:
 * all water from Alamito Creek, Terlingua Creek, Pecos River, Goodenough Spring, Devils River, San Felipe Creek, Pinto Creek;
 * remaining third from the tributaries where Mexico gets $1/3$ as mentioned above;
 * remaining half below the lowest major international storage dam;
 * half of the otherwise unallocated flows between Fort Quitman and the lowest major international storage dam.

Mexico's water debts
The first major problem with the treaty surfaced in the 1992-1997 cycle: a drought had forced Mexico to reduce deliveries. However, the extraordinary drought was not declared at the time, so Mexico, still in debt, declared it unilaterally in 1999 and postponed the deliveries into the next cycle. The U.S., after an original protest, agreed in 2002 to roll over the deficit into yet another (third) 5-year cycle. The U.S. stated that international obligations have the highest priority on the river, and storing the water in the upstream tributaries for domestic use is not acceptable. By 2004, Mexico delivered on 75% of its debt.

The 2020-2025 cycle exhibited similar problems, with Mexico delivering just one year's worth of water (400,000 acre-feet) by mid-2024. The previous cycle that ended on 25 October 2020 was also running with a deficit until a last-minute deal ("Minute 325", October 2020) lead to delivery of water by Mexico. The Minute 325 also envisioned signing of a deal for the new cycle by December 2023, however, Mexico refused to sign the new Minute due to domestic opposition in Chihuahua. In any case, it is unclear if Mexico can meet its obligations due to very low levels in the La Boquilla and Francisco Madero reservoirs.