Eighty years ago, the United States and Mexico worked out an arrangement to share water from the two major rivers that run through both countries: the Rio Grande and the Colorado. The treaty was created when water wasn't as scarce as it is now.
Water from Mexico flows to Texas' half-billion-dollar citrus industry and dozens of cities near the border. On the Mexican side, some border states like Baja California and Chihuahua are heavily reliant on the water that comes from the American side of the Colorado River.
Now, those water-sharing systems are facing one of the biggest tests in their history. Mexico is some 265 billion gallons of water behind on its deliveries to the United States.
Unpredictable weather patterns due to climate change, growing populations, aging infrastructure and significant water waste have left both countries strapped for water and have escalated tensions along the border.
Maria-Elena Giner is the U.S. commissioner of the International Boundary and Water Commission, the binational agency that oversees the 1944 water treaty and settles disputes.
Mexico is "at their lowest levels ever" in the treaty's history, Giner said. The treaty operates in five-year cycles, and the current deadline for deliveries isn't until October 2025.
But "the question is that they're so far behind, it will be very difficult, if not statistically impossible, for them to make up that difference," Giner said.
Victor Magaña Rueda, an environmental scientist at the National Autonomous University of Mexico, said neither country can survive without the other's water. He called the 1944 treaty a first step.
"Now we have to probably think of how we manage water and each side to adapt to those changes that we are experiencing in terms of climate," Rueda said.
Tensions rise in the U.S.
Already, Texas' last sugar mill shut down this year due to lack of water, lawmakers from the state have said. Now, officials don't want the same thing to happen to the state's citrus industry, concentrated in the Lower Rio Grande Valley, and to other agricultural activities dependent on Mexican water.
Ten lawmakers from a bipartisan congressional delegation urged the U.S. Congress to withhold appropriations of money and assistance to Mexico — outside of funds for border control — until it delivers the needed water.
"Farmers and ranchers across South Texas remain under continued financial strain and could suffer a similar fate as the sugar industry, should Mexico continue withholding water," the lawmakers wrote in May. "Additionally, the lack of reliable water delivery affects municipalities and threatens the quality of life for many American citizens living along our border."
Rep. Henry Cuellar, a Texas Democrat, signed the letter. He said this isn't the first time he has witnessed Mexico falling behind on water deliveries.
But the unpredictability of this cycle has created significant hardship for members of his congressional district in the southwest tip of Texas along the Rio Grande.
"Mexico has not even responded to this, which means one thing to me," Cuellar said last month about the letter. "That means that the possible loss of money is probably less important than the water right now for their communities. Their silence tells you that they're more interested in water than money right now."
Rep. Monica de la Cruz, a Texas Republican and another Texas representative who signed the letter, spoke before Congress in May to emphasize the loss of agriculture and industry in South Texas.
"If we cannot save our farmers, then Mexico does not deserve to have any money appropriated to them," the Republican said. "We want our water — we demand our water."
To be sure, Congress hasn't yet funded the government for the next fiscal year, which begins in October, and could take up a temporary stopgap bill to avert a shutdown. So the threat of financial loss to Mexico remains more theoretical at this point.
As urgent as receiving water from Mexico may seem, it isn't the only water problem for Texas. In Texas and several other states across the U.S., a significant amount of water is wasted from infrastructure breaks and leaks.
The state lost an estimated 129 billion gallons of water in 2022 — the latest figures available from water-loss audit data submitted by public water suppliers to the Texas Water Development Board.
Water politics in Mexico
To address the water scarcity in Texas, officials last year proposed a solution: a treaty "minute," or amendment, that would allow Mexico to pay water directly to South Texas instead of giving two-thirds to the Mexican state of Tamaulipas first, as currently specified in the treaty.
But quenching the thirst in South Texas ahead of its own citizens was likely a nonstarter ahead of Mexico's presidential election this year.
Negotiations on the treaty changes were completed and both countries were set to sign last December, but Mexico has yet to receive official authorization to do so, said Giner, of the International Boundary and Water Commission.
Several Mexican officials contacted for this story declined to comment on the record about Mexico's water deliveries to Texas and future treaty negotiations.
But on Mexico's side of the border, the country is facing its own water issues, beyond water battles with the United States. A crisis in Mexico City this year left many of its 22 million residents without clean water as the city prepared for the possibility of running out.
These strains, along with rapidly growing populations, have put the country severely behind on its water deliveries to the United States.
In April, Mexico's current president, Andrés Manuel López Obrador, said that the country will focus on guaranteeing water for its residents.
"Priority must be given to domestic water, which is consumed by people rather than by companies," he said. "We are looking for a way to address the problem of drought, of water shortages — work is being done."
The new president-elect, Claudia Sheinbaum, is expected to take a similar approach when she takes office in October, Rueda, the environmental scientist, said.
Troubles ahead of last election
This five-year cycle isn't the first time Mexico has fallen behind on providing water to the United States.
Toward the end of the last cycle, which concluded just days before the 2020 U.S. presidential election, Mexico had delivered most but not all of its water to the United States.
Mexico tried to pull water from a dam in Chihuahua state but was unsuccessful. Three days before the official deadline, Mexico and the U.S. agreed to a minute that permitted Mexico to transfer to the U.S. the water in the Amistad and Falcon reservoirs along the border to avoid a shortfall.
But that transfer of reservoir water nearly depleted all of northern Mexico's stored water resources, making the country even more vulnerable to future disruptions.
For this current cycle, if Mexico is unable to deliver all its water, the treaty allows for a water debt to be carried over for one cycle.
So if Mexico doesn't catch up by the end of this cycle, it can repay its debt by the end of the following one. Minute 234 stipulates that neither country may accrue a shortfall for two consecutive five-year cycles.
Rueda, the environmental scientist in Mexico, said some farmers in Mexico want the treaty with the U.S. to be dissolved because they need the water for their crops.
But doing so would be disastrous for residents of both countries as a whole.
"If we stop the treaty, then it will mean a real disaster for that region, just because of the selfishness of a few," he said.
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