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The Colorado River currently supports 40 million people and $1.4 trillion in annual economic activity in seven U.S. states and Mexico — but it was never intended to be stretched so thin.

A century-old legal framework promises those users more water than there is to go around. The river’s flow has shrunk by about 20 percent over the last century as climate change has made the West more arid. As water has vanished, states have clashed over how to divide up what remains. The core dispute is between the sparsely inhabited mountainous states of the “Upper Basin,” where hay farmers and a few major cities like Denver draw water from the river and its tributaries, and the far more populous “Lower Basin,” which diverts water to support most of the nation’s winter vegetable farmers as well as megacities like Los Angeles and Phoenix.

San Diego appears to be on the verge of long-sought water sales that officials hope will at least reduce future cost increases to local customers. Whether that lowers the political temperature between the city of San Diego and the San Diego County Water Authority over rates remains to be seen.

Dan Denham, general manager of the water authority, said in the coming months the agency expects to close deals to send water to a handful of fellow members of the Los Angeles-based Metropolitan Water District of Southern California.