It’s a question that keeps coming up as California’s drought drags on: What should cities and water agencies do about the most egregious water wasters?

You know them. The neighbor always hosing down the sidewalk. The rich guy who waters his lawn every day and laughs at the fines. The callous guzzler, thumbing his nose at the rest of us dutifully putting buckets in our showers.

Well, water providers have a secret weapon. It’s called a flow restrictor.

A 2-inch-long brass cylinder, the modest-looking plumbing device is to water wasters what handcuffs are to shoplifters and parking boots are to motorists piling up unpaid tickets. And now water agencies struggling to meet California’s tough new conservation rules have the devices at the ready and are giving them a fresh look.

“It’s like shutting down three lanes of traffic on a four-lane freeway,” said Brian Dunbar, a distribution manager with San Jose Water Co. “You have to slow down.”

The way they work is simple: Utility employees can clamp flow restrictors onto the water meters of habitual water hogs, dramatically limiting the amount of water that flows to the property from the main pipe under the street.

From the East Bay to the Peninsula to the Santa Clara Valley, water agencies have the devices. And while they say they haven’t had to unleash them yet, they are ready to do so during the hot summer months if necessary.

Water guzzlers who are served by the East Bay Municipal Utility District can be curbed with a restrictor after three warnings.

“The flow is basically just for the essentials. But it’s annoying. It would drive anybody crazy,” said district spokeswoman Andrea Pook.

San Jose Water, a private company that serves 1 million people in San Jose, Los Gatos, Saratoga and other Silicon Valley communities, included flow restrictors as part of the regulations it put in place June 15 to get its customers to cut water use 30 percent.

Its devices can cut water flow by 72 percent — from the typical 18 gallons a minute at most homes to 5 gallons per minute. The rules allow the company, after one written warning, to install a flow restrictor on the meter “of any customer observed by utility personnel to be using water for any nonessential or unauthorized use.”

Those violations include wasting water — not going over monthly limits, but repeatedly doing things such as watering lawns more than two days a week, hosing down pavement or washing cars.

In the month since the new rules took effect, San Jose Water hasn’t slapped the devices on anybody’s meter, company spokesman John Tang said.

Under current practices, the company’s customers who waste water will get a door hanger asking them to stop. After a second violation, they are sent a letter. The third offense brings a personal visit from a water company employee. On the fourth offense, their meter can be fitted with a flow restrictor and they are subject to a fine, which varies depending on which city they live in. For San Jose residents, it’s $160.

There’s also a $45 fee when the flow restrictor comes off, and anyone who tries to take it off themselves, like Homer Simpson stealing cable TV, is subject to having their water shut off.

“Water is a finite resource, and we want folks to use it judiciously,” Tang said. “At the end of the day, we are trying to get everybody to follow the rules. Everybody needs to contribute to conserving.”

In May, San Jose Water customers reduced their water use an impressive 36 percent compared with May 2013, the baseline year.

Pook said EBMUD, whose customers cut water use 31 percent in May, has not had to unleash the restrictors on anybody yet. The district did use them in previous droughts. Famously in 1977, as TV cameras and newspaper photographers recorded the moment, the district clamped one on the home of Raymond and Phyllis Olson, a Hayward couple who were using 883 gallons a day.

“It’s used if a customer is being unreasonably and willfully wasteful,” Pook said. “We don’t want to get to that point, but if it does we need that tool. It’s the last straw.”

Some Bay Area residents are urging water agencies to pull out the devices now and use them aggressively.

“They have to use them on everybody fairly, even on rich people and corporations,” said Lisa Wyatt, of San Mateo, who gets mad when she sees Silicon Valley companies along Highway 101 continuing to drench their grass.

“There are people who feel they are above it all,” she said. “My mother always said if you want to get somebody’s attention you have to hit them between the eyes with a two-by-four.”

But some say the most bullheaded water wasters may not be deterred.

“If you reduce the flow by 70 percent, what would prevent someone from running their sprinklers four times as long?” said David Sedlak, a UC Berkeley engineering professor and water expert. “Appealing to people’s sense of community and public shaming is usually enough.”

San Francisco has flow restrictors and a rule that can slap water wasters with a $245 fee to install one. South Bay and Peninsula cities, including Mountain View, Menlo Park and Sunnyvale, also have the devices and drought rules enabling their use. But they have mostly been meeting conservation targets and haven’t yet had to resort to the nuclear option.

But water agencies will use them if they need to, particularly if the drought drags on several more years, said Gary Kremen, chairman of the Santa Clara Valley Water District.

“If somebody is the worst of the worst and they are just ignoring everything, I think it’s another tool in the tool kit,” he said. “I really think we have to have carrots, but I’m a believer that we need sticks also.”

Paul Rogers covers resources and environmental issues. Contact him at 408-920-5045. Follow him at Twitter.com/PaulRogersSJMN