It’s carrot-planting time in California. In the small town of New Cuyama, that means a war over water. Little farmers take big farmers to court.

People in New Cuyama know their neighbors. The school secretary doubles as a bus driver. A vegetable grower also shoes horses. New Cuyama has a small market, hardware store, and miles of land sown with olives, pistachios, grapes, and carrots. When rainfall is scarce, growers there rely on underground water. And small farmers complain that big carrot growers hog too much of it.

Do you have baby carrots in your fridge even in winter? Most people want these tasty little nubs available all year long. And that keeps big California carrot growers like Grimmway Farms busy. Along the highway in New Cuyama, sprinklers douse Grimmway’s fields for eight hours straight. Then the growers turn off the waterworks. The fields dry for two weeks. Carrot roots stretch downward in search of moisture.

“We feel we are being totally overrun by those people,” says Jean Gaillard of the big growers. “They are taking all the water.” Mr. Gaillard sells produce from his garden to locals. Dry weather puts him in a tight spot. His well water has dropped 30 feet in the past two decades. Groundwater levels shrink. The cost to pump water rises.

But large growers have good reason for farming in New Cuyama. Jeff Huckaby is the president of Grimmway. “It’s one of the best carrot-growing regions that we’ve come across,” he says. Dry areas like New Cuyama are a sweet spot for carrots. They encourage carrot roots to grow long as they reach below the surface for moisture. “The soil up here is ideal,” Mr. Huckaby says.

So whatever you wish that others would do to you, do also to them. — Matthew 7:12

Why? Groundwater is an essential resource we must all learn to steward well and share.