Yes, Virgina, it rains it California

The wine grapes we are familiar with, vitis vinifera, had its origins in the high desert of the Middle East.  They're a desert plant.  They don't require tons of water.  As a matter of fact, many vineyards are, "dry farmed" without any inrrigation!

That doesn't meant they don't need water.  They rely on winter rains to soak into the ground so they can go looking for it.  Grape vines are the second deepest rooted plant on Earth.  If they are thirsty enough they'll dig down 30 feet!

The short story is that too much water makes for lazy grapes.  Lazy grapes don't taste great.  So growers know that if the vines are a bit "stressed" then they will produce taster grapes.

"We don't dry farm in order to save water," Leeds (a Rutherford grower) said. "If we thought we could have more productive or healthier vines, we'd water. Yes, we're concerned with the environment, but we make more flavorful grapes and more flavorful wine by farming organically and dry farming."