Arizona and Nevada are pursuing agreements with the San Diego County Water Authority (SDCWA) to siphon off its share of the Colorado River. In exchange, the states would fund the quarterly costs of running San Diego's Carlsbad Desalination Plant.

It's the largest seawater desalination plant in North America, and supplies 54 million gallons of drinking water for the city and county every day.

It was built following a 5-year drought that pushed San Diego County to the absolute limit. By the time it ended in 1992, the county had lost one-third of its water resources, and imports, tanked and bottled, had to come in to make up the difference.

Following the drought, the SDCWA sought insurances against such a disaster, by building the desalination plant, but also increasing the height of a major dam wall to store more water, and acquiring the rights to a major Colorado River allocation that had been conserved for a farming district.

These strategies reduced the county's reliance on imports from 95% to 10%. Such substantial investments mean the SDCWA now has the opportunity to help its neighbors. By relinquishing part of its share in the Colorado River, 500,000 people in Nevada and Arizona would have access to clean water in case of drought.

"This agreement could be a gamechanger for San Diego County and the entire Southwest because it creates the possibility of a new, collaborative path for moving water where it's needed most while keeping reliability and affordability at the center for ratepayers," said Water Authority Board Chair Nick Serrano in a statement.

"Leveraging existing resources like our Carlsbad desalination plant in this moment simply makes sense for everyone."