Marc Mondavi is standing in the middle of his vineyard, talking to two copper rods. Find water," he tells them as he walks slowly down a row of vines holding the rods pointed in front of him. As if possessed, the rods start moving until they cross over one another. "Here," he says. "Here's where the water is." Yeah, right. Isn't the whole ... thing a little undignified for a descendant of California wine royalty - not to mention the vice president of Charles Krug Winery? Try telling that to grape growers in Northern California, who repeatedly call on Mondavi to seek out water for their industrial-size wells. "I don't know how he does it, and I'm not going to learn," said John Franzia, whose Bronco Wine Co. in Ceres (Stanislaus County) grows 40,000 acres of grapes. "But I'm a believer because I have water." Franzia has 300 wells on his various properties, and Mondavi told him where to drill a number of them. Rombauer Vineyards, maker of a famous Chardonnay, uses him. Patriarch Koerner Rombauer even had rods custom-created for Mondavi. When Carmen Policy, former president and CEO of the San Francisco 49ers, bought property in Yountville contingent on finding water, Mondavi was called in. He found a gusher. He's a bona fide water witch - someone who can find groundwater without the use of science. It's also known as water dowsing, divining or doodlebugging. Oftentimes dowsers use forked willow, peach or witch hazel branches as divining rods. It is speculated that there are thousands of dowsers operating in the United States.