The punishing drought that has swept California is now threatening the state's drinking water supply. With no sign of rain, 17 rural communities providing water to 40,000 people are in danger of running out within 60 to 120 days. State officials said that the number was likely to rise in the months ahead after the State Water Project, the main municipal water distribution system, announced on Friday that it did not have enough water to supplement the dwindling supplies of local agencies that provide water to an additional 25 million people. It is first time the project has turned off its spigot in its 54-year history.

State reservoir levels are lower in California than they were at this time in 1977, the last time the state endured a drought this severe.

(Read more: World's cities face big extreme weather risk)

State officials said they were moving to put emergency plans in place. In the worst case, they said drinking water would have to be brought by truck into parched communities and additional wells would have to be drilled to draw on groundwater. The deteriorating situation would likely mean imposing mandatory water conservation measures on homeowners and businesses, who have already been asked to voluntarily reduce their water use by 20 percent.

Alice Cahill | Flickr | Getty Images

"Every day this drought goes on we are going to have to tighten the screws on what people are doing" said Gov. Jerry Brown, who was governor during the last major drought here, in 1976-77.

This latest development has underscored the urgency of a drought that has already produced parched fields, starving livestock, and pockets of smog.

"We are on track for having the worst drought in 500 years," said B. Lynn Ingram, a professor of earth and planetary sciences at the University of California, Berkeley.

Already the drought, technically in its third year, is forcing big shifts in behavior. Farmers in Nevada said they had given up on even planting, while ranchers in Northern California and New Mexico said they were being forced to sell off cattle as fields that should be four feet high with grass are a blanket of brown and stunted stalks.

(Read more: California's 2-year drought—it's what's for dinner)

Fishing and camping in much of California has been outlawed, to protect endangered salmon and guard against fires. Many people said they had already begun to cut back drastically on taking showers, washing their car and watering their lawns.

Rain and snow showers brought relief in parts of the state at the week's end — people emerging from a movie theater in West Hollywood on Thursday evening broke into applause upon seeing rain splattering on the sidewalk — but they were nowhere near enough to make up for record-long dry stretches, officials said.

"I have experienced a really long career in this area, and my worry meter has never been this high," said Tim Quinn, executive director of the Association of California Water Agencies, a statewide coalition. "We are talking historical drought conditions, no supplies of water in many parts of the state. My industry's job is to try to make sure that these kind of things never happen. And they are happening."

Officials are girding for the kind of geographical, cultural and economic battles that have long plagued a part of the country that is defined by a lack of water: between farmers and environmentalists, urban and rural users, and the northern and southern regions of this state.

More from the New York Times: Parched, California cuts off tap to agencies

Severe drought grows worse in California

Colorado river drought forces a painful reckoning for states "We do have a politics of finger-pointing and blame whenever there is a problem," said Mr. Brown. "And we have a problem, so there is going to be a tendency to blame people." President Obama called him last week to check on the drought situation and express his concern.

Tom Vilsack, secretary of the federal Agriculture Department, said in an interview that his agency's ability to help farmers absorb the shock, with subsidies to buy food for cattle, had been undercut by the long deadlock in Congress over extending the farm bill, which finally seemed to be resolved last week.

Mr. Vilsack called the drought in California a "deep concern," and a warning sign of trouble ahead for much of the West.

"That's why it's important for us to take climate change seriously," he said. "If we don't do the research, if we don't have the financial assistance, if we don't have the conservation resources, there's very little we can do to help these farmers."