A water dispute between the United States and Mexico that goes back decades is turning increasingly urgent in Texas communities that rely on the Rio Grande. Their leaders are now demanding the Mexican government either share water or face cuts in U.S. aid.

In a deepening diplomatic conflict, Mexico is behind in obligations under an 80-year-old treaty that governs cross-border flows of the drought-stricken Colorado River. It has for decades resisted water deliveries to the United States from its reservoirs in the Rio Grande basin as it faces its own drought pressures on thirsty and valuable crops bound for sale across the border.