The most cost-effective way to conserve the dwindling waters of the Colorado River may not come from building new reservoirs, canals, or wells, but from changing how water is used on farms that consume most of it.
That's the conclusion of a comprehensive study by UC Riverside's School of Public Policy, conducted with the Utah Rivers Council.
Led by UCR graduate student Paloma Avila, the study examined 462 federally funded Colorado River conservation and supply projects, totaling about $1 billion (in 2023 constant dollars) between 2004 and 2024, using available spending data from the U.S. Bureau of Reclamation.
It found that agricultural conservation programs saved water as low as $69.89 per acre-foot, while new supply efforts—such as reservoirs, wells, and wastewater treatment facilities—cost more than $2,000 per acre-foot on average. In water conservation, an acre-foot is a measure of the amount of water required to cover one acre of land to a depth of one foot, or approximately 325,851 gallons.
"It's important to understand where investments in conservation are being made across the Colorado River Basin and to evaluate their effectiveness," Avila said.
The study has broad implications because the Colorado River is the economic lifeblood for agriculture in seven states while providing water for as many as 35 million people in and out of the basin.
The UCR analysis showed that the greatest savings occurred where most of the river's water is used, said Mehdi Nemati, an assistant professor of public policy, co-author of the study, and Avila's faculty advisor.
"Eighty percent of the water in the basin is consumed by agriculture," Nemati said. "Agricultural conservation—particularly incentive programs—gives us the lowest cost with the highest savings."
The vast scale of agricultural water use includes maintaining pasture grasses and alfalfa crops, grown for cattle feed, that cover wide stretches of Wyoming, Colorado, and Arizona. Keeping those fields green often means flooding entire parcels.
Nemati explained that paying ranchers and farmers to cut back on such practices, even temporarily, can deliver meaningful water savings at relatively low cost.
In California's Palo Verde Valley and parts of Arizona, federal funds have been used to pay farmers to leave alfalfa fields unplanted for a season or two. Other programs encourage "deficit irrigation," in which growers intentionally use less water while still harvesting a crop. Subsidies have also supported growing other crops and replacing flood irrigation with sprinkler or drip systems that deliver water with much greater precision.
The findings, Nemati said, are particularly useful for policymakers.
"If the goal is to prioritize limited funding, then projects with the highest cost effectiveness make the most sense—especially in agriculture," he said.
