LOS ANGELES — California’s record drought has unleashed a flood of social-media tattletales.

Vigilantes armed with cameraphones prowl neighborhoods from San Diego to San Francisco documenting sprinklers running freely, runoff flowing from saturated lawns and other water- wasters. Sacramento, California’s capital, received almost 12,000 reports of excessive water use in the first six months of this year, up from about 800 in the period last year.

With four-fifths of the state in extreme drought, Californians have been asked to cut consumption by 20 percent. When state officials announced that water use in May instead rose by 1 percent, “drought shaming” took off through social media such as Twitter’s microblogging platform and VizSafe, a virtual neighborhood watch application.

“There’s a perspective of, ‘I’m following the rules, so I should hold other people accountable for following the rules,’ ” said Peter Mottur, chief executive officer of Middletown, Rhode Island-based VizSafe, whose crowdsourcing platform overflows with reports of people hosing down sidewalks, watering lawns in midday and other infractions. “I wouldn’t call it tattletale. It’s more about civic responsibility.”

Farmers in the state that produces almost half of the fruits, vegetables and nuts consumed in the U.S. have left unplanted an estimated half-million acres for lack of water. Most reservoirs are a fraction of their normal size, surrounded by barren rings that have grown as the water receded. Cities from San Diego to Montague, near the Oregon border, limit lawn watering and have told restaurants not to serve water unless requested.

Yet responses to the drought vary widely. Folsom, a Sacramento suburb, used 30.7 percent less water in May than the average of the three years that ended in 2013, according to the state Water Resources Control Board and Marcus Yasutake, the city’s water-resources director. San Juan Capistrano, the Orange County suburb famous for its mission, used 36.5 percent more water, according to the state board. The increase was partly because a golf course switched from its own wells to the municipal system, said Francie Kennedy, the community’s water conservation coordinator.

The control board in July approved fines of as much as $500 on people who wash down sidewalks and driveways, let water from lawns and landscaping overflow into the streets, and wash cars without shutoff nozzles on their hoses.

Mike Budd, 26, an actor and musician in the Brentwood neighborhood, said his roommate drought- shamed him in 2012 for not using a shutoff valve to hose off his car. Now, Budd said, he’s doing the same thing himself, posting about three items a week on VizSafe calling out others for letting runoff from lawns pool in the street.

“A $500 fine may have very little impact on someone who just wants to keep their lawn green,” Budd said by telephone, “but people around here do care about their reputations.”

A VizSafe user who goes by the name Agua Caliente posted photos of a nursery east of Los Angeles with sprinklers running during the day and a bar in Pasadena with misters cooling the patio in the afternoon.

The bar, Kings Row Gastropub, used mist machines on Aug. 2 to offer relief from 86-degree Fahrenheit (30-degree Celsius) heat. The manager, James Fraley, said he doesn’t begrudge the self-appointed cop, though he said Agua Caliente doesn’t have the full picture. Savings from the kitchen’s low-flow dishwasher far outweigh the small spraying from the misters, Fraley said.

“We believe in being responsible and taking care of the world, but we also believe in taking care of our customers when it’s hot outside,” Fraley said.

Officially, California’s Water Resources Control Board isn’t endorsing the activities of self-appointed water cops.

“We encourage residents who have concerns about a neighbor to either talk to the neighbor, or at least go to the urban water supplier in that area,” spokesman George Kostyrko said.

That’s happening too. Of the almost 12,000 reports of water waste received in Sacramento in the first half of 2014, more than 3,700 led to written warnings, said Jessica Hess, a spokeswoman for the city utilities department. The enforcement helped decrease Sacramentans’ water use by 22 percent in July compared to July 2013, she said.

In Los Angeles, where some freeway signs now flash water- conservation messages instead of traffic alerts, the message is lost on many residents. California’s largest city reported a 9.2 percent increase in water use in May compared with the average May from 2011 to 2013 in the statewide survey.

Los Angeles authorities who once relied on telephone tipsters now also scour social media. Los Angeles has received 30,000 complaints of excessive water use since 2009, with just 300 cases resulting in fines.

Chris Rexroad, 30, a resident of the Silverlake neighborhood, said he was shocked to see the dry bed of Owens Lake, one of Los Angeles’ historic water sources, during a visit to the eastern Sierra. Yet Rexroad said he hasn’t curtailed his own water use.

“I still water my plants at home and take the occasional lengthy shower,” he said.

The situation is different in some northern and central parts of the state that are on the verge of running out of water. Systems serving about 3,900 people are in danger of going dry “if action is not taken immediately,” according to the state’s Public Health Department.

The largest of those communities is Montague, a ranching town of about 1,500 people, 20 miles south of the Oregon border. Lake Shastina, a reservoir on the Shasta River, doesn’t have enough water to supply the town past Sept. 1.

Montague secured $1.3 million in state funding to replenish the lake with groundwater from wells pumped into the Shasta River, said Chris Tyhurst, the town’s water manager. The fix should work in time avoid having to truck in water from neighboring Yreka, he said.

Meanwhile, Montague residents have reduced water use by two-thirds, to 3 million gallons in June from the usual 9 million, and brown lawns are the norm in the community, he said.

The Siskiyou County community is meanwhile facing another threat from the drought: Lightning from a single storm touched off at least 26 fires in the tinder-dry forests, according to the U.S. Forest Service.

“We have fires around here and it’s getting in people’s lungs and everybody’s irritable,” Tyhurst said. “This has not been a good summer.”