The area around Placerville in northern El Dorado County, where Mr. Mansfield is, has been spared the worst of the drought. He credits this to forward-thinking planners of the El Dorado Irrigation District, who secured rights to a series of reservoirs around the turn of the century.

“Even though the drought has been severe here, we have a very good water supply now with no restrictions,” he said.

It’s a different story in the southern part of the county, which depends on wells. In Somerset, about 12 miles southeast of Placervile, Hank Beckmeyer and Caroline Hoel of La Clarine Farm have a few acres of grapes around their house. They follow the minimalist teachings of the Japanese agronomist Masanobu Fukuoka, who counseled a hands-off approach to farming. Right now, it seems like a losing proposition.

“The Fukuoka thing works great if you’re not into your fourth year of drought,” Mr. Beckmeyer said. “We lost some young vines that couldn’t handle the dryness. We only have one well for the house and the winery. This year the grapes are on their own.” Fortunately, La Clarine has a steady supply of grapes they buy from farmers who are better situated, from which they continue to make excellent wines.

Geography is destiny, too, back in the Paso Robles region, where Tablas Creek Vineyard, about 20 miles northwest of AmByth Estate, has not had nearly as many water problems. Like AmByth, Tablas Creek largely practices dry-farming through its 105 acres of vines. Because the western part of Paso Robles receives much more rain than in the east, the vineyard has managed to thrive. Even though the winter rains have been half the normal 28 inches since the drought began in 2012, it’s been enough to replenish the supply of groundwater.

“The vineyard looks great, particularly the dry-farmed blocks,” said Jason Haas, a partner and general manager of Tablas Creek. “Those relying on water falling from the sky are in better shape than those relying on pumping from the ground or Sierra runoff.” Even so, Tablas Creek conserves where it can, using Sloan water-free urinals in the men’s room at its solar-powered winery.