Never mind long showers, leaky toilets, or even sprawling golf courses. Agriculture is the biggest user of water in the world. Every year, the U.S. government spends millions and millions of dollars to help farmers make their irrigation more efficient. 
In many cases, the goal is to reduce the amount of water diverted from rivers so that more remains for other users, including nature. But the subsidy can backfire in the long run.
“This policy is a real problem,” said Ray Huffaker, an economist at Washington State University in Pullman on Friday at a session called, “Water Crisis in Agriculture: How to Produce More with Less.” Attempts at conservation sometimes leave less water behind, Huffaker says...
(Photo: Jeff Vanuga/USDA)
According to his analysis, here’s what happens: With inefficient irrigation techniques, such as intentional flooding, water runs off and soaks back into the ground to recharge underground supplies in aquifers. “This water goes to work after it leaves the farmer’s fields,” Huffaker said.
Farmers can put more of that water to work growing crops by using techniques such as drip irrigation. When they do, though, aquifers suffer. Even if farmers end up diverting less water from the river, Huffaker’s model showed, the environment suffers a net loss.
“This is a significant point,” says John Letey, who directs the Center for Water Resources at the University of California, Riverside. He says that water planners often overestimate how much water will be saved by making irrigation more efficient. “It’s not neccesarily a gain.” However, in places where agricultural runoff is polluted, by salt or selenium, for example, it may make sense to increase efficiency and avoid sending leftover water into streams or aquifers.
