It has been two decades since Willie Hartman started making farm equipment that helps growers conserve water, but sales didn’t take off until the past four years. Credit goes, in part, to California’s worst drought in at least half a century.

Farmers in the Golden State’s $45 billion agricultural economy are increasingly thirsty for ways to save water, prompting a burst in demand for tools and processes like Mr. Hartman’s On Target Sprayer.

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