WATER SECURITYWater Wars: A Historic Agreement Between Mexico and US Is Ramping Up Border Tension
As climate change drives rising temperatures and changes in rainfall, Mexico and the US are in the middle of a conflict over water, putting an additional strain on their relationship. Partly due to constant droughts, Mexico has struggled to maintain its water deliveries for much of the last 25 years, deliveries to which it is obligated by a 1944 water-sharing agreement between the two countries.
As climate change drives rising temperatures and changes in rainfall, Mexico and the US are in the middle of a conflict over water, putting an additional strain on their relationship.
Partly due to constant droughts, Mexico has struggled to maintain its water deliveries for much of the last 25 years, in keeping with a water-sharing agreement between the two countries that has been in place since 1944 (agreements between the two regulating water sharing have existed since the 19th century).
As part of this 1944 treaty, set up when water was not as scarce as it is now, the two nations divide and share the flows from three rivers (the Rio Grande, the Colorado and the Tijuana) that range along their 2,000-mile border. The process is overseen by the International Boundary and Water Commission.
Mexico must send 430 million cubic meters of water per year from the Rio Grande to the US, while the US must send nearly 1.85 billion cubic meters of water from the Colorado River to support the Mexican border cities of Tijuana and Mexicali.
Water deliveries are measured over a five-year cycle, and the current one ends in October. Mexico struggled to deliver its water “debt” in the last cycle which ended in 2020, using waters from reservoirs at the last minute to fulfil its obligations. This left northern Mexico with severely depleted water levels.
Due to growing tensions over water, the Biden administration tried to negotiate and work with the Mexican government to improve the speed with which Mexico’s water deliveries were taking place in 2024.
But with Donald Trump’s return to office, the US has taken a more aggressive stance with Mexico to address its water debts to the US. For the first time in over 50 years, in March of 2025, the US refused to send water from the Colorado River to Tijuana – a city of nearly 2 million people – in order to force Mexico to send more water to Texas.
Mexico has since responded by transferring 75 million cubic meters of water, but this is just a drop in the bucket, as Mexico remains 1.5 billion cubic meters in debt. And this did little to satisfy the Trump administration, which threatened to withhold more water from Mexico. It also demanded the resignation of Maria-Elena Giner, who led the International Boundary and Water Commission, in April.
