Most of that water goes toward irrigation. But some goes to the winery itself and comes out as waste. On average, wineries create 6 gallons of wastewater for every gallon of wine, which means that in 2010, the California wine industry produced enough to drown Golden Gate Park in more than 8 feet of runoff. About one-fourth of the industry's waste is produced at this time of year, during harvest.

According to Sheldon Sapoznik, Napa County's land use development supervisor, wastewater mainly comes from washing tanks, barrels, crush pads and floors. No matter the use, it's wastewater that needs to be dealt with.

It's not hard to imagine a solution. Wineries all own vineyards or buy from them. Vineyards need water.

Problem solved, right?

Not quite. Microbes can break down the grape juice and plant matter flushed into the water, but they need oxygen to do it. That's not the problem. The problem is how much oxygen those microbes need, a measurement called biochemical oxygen demand (BOD). In winery waste, there's not nearly enough supply for that demand.

"Winery wastewater obviously has lots of suspended solids," Sapoznik says, "and that means there's a lot of BOD. We require that BOD be down to less than 50 before irrigation."

High sugar content

Winery wastewater's high sugar content can result in a BOD anywhere from 2,500 to 10,000. By comparison, human sewage registers at a mere 150 to 300.

Dump high-BOD waste in the ground near a waterway, and you wreak havoc - not because of toxins but because the waste drains oxygen from the water, which means it's not available to other life.

"It puts a big slime layer on a creek," says Sapoznik, "and it'll kill fish much faster than if it were a sewer line."

Even wineries far away from rivers can't irrigate with wastewater. That same oxygen demand will starve microbes that help vine roots absorb water and nutrients.

Some wineries have an easy out: Dump wastewater into the same sewer system that their residential neighbors use. But the spike in use can exceed sanitation department thresholds, which translates to big bills. And then a winery can't use that water in the vineyards. Any winery that wants to reclaim the water for irrigation must effect a 50- to 200-fold drop in BOD while navigating government regulations around wastewater.

This has created a thicket of potential options, which firms such as Santa Rosa's Summit Engineering help wineries to navigate.

"The most common treatment method is a pond," says Anu Shah, manager of the company's water and wastewater division. You've probably seen these ponds on Wine Country back roads: big pools of water with large motors that aerate the liquid. Pump wastewater in; release clean water 60 to 90 days later.

"Those kinds of systems are simple to operate," says Shah.

But ponds take up space that could be used for grapes. And neighbors don't like them: They're unattractive, they're noisy and they smell.

Wineries that prefer a more discreet option might try leach fields, says Shah - set up a septic tank and occasionally flush it into an underground set of pipes with tiny holes drilled along their lengths. Water trickles into the ground at a rate slow enough for bacteria to break down solids without getting starved for oxygen. But a leach field system works only in certain soil types, and the treated water isn't available for irrigation.

An option making inroads into Napa, however, is a hydrate system - a tank with filters that remove big solids and oxygen pumps that let microbes break down the rest. Perhaps its biggest asset: It doesn't take up much space.

"It was upsetting to me to take our land and use it for wastewater ponds," says Chuck Wagner, winemaker for Caymus and Conundrum.

But those were the rules if your effluent reached a certain volume.

"We looked all around for different methods," he says. "There are a lot of systems out there, but there was only one that would pass muster in Napa."

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