LOS ANGELES — Faced with a persistent drought and the threat of tighter water supplies, Los Angeles plans to begin using heavily cleansed sewage to increase drinking water supplies, joining a growing number of cities considering similar measures.

Mayor Antonio R. Villaraigosa, who opposed such a plan a decade ago over safety concerns, announced the proposal on Thursday as part of a package of initiatives to put the city, the nation’s second largest, on a stricter water budget. The other plans include increasing fines for watering lawns during restricted times, tapping into and cleaning more groundwater, and encouraging businesses and residents to use more efficient sprinklers and plumbing fixtures.

The move comes as California braces for the possibility of the most severe water shortages in decades.

Snowfall in the Sierra Nevada, which supplies about a third of Los Angeles’s water, is short of expectations. At the same time, the Western drought has lowered supplies in reservoirs, while legal rulings to protect endangered species will curtail water deliveries from Northern California.

Worsening the problem, Los Angeles is expected to add 500,000 people by 2030, forcing the city to examine new ways to meet demand. One option off the table, Mr. Villaraigosa said, is a repeat of the city’s troubled history, fictionalized in the movie “Chinatown,” of diverting a distant river southward to slake the city’s thirst.

The city, pushed by legal claims, is already paying millions to restore dried-up portions of the river, the Owens.

“There simply are no more holes or straws to pitch,” Mr. Villaraigosa said at a news conference at a water plant.

Many cities and towns across the country, including Los Angeles, already recycle wastewater for industrial uses and landscaping.

But the idea of using recycled wastewater, after intense filtering and chemical treatment, to replenish aquifers and reservoirs has gotten more notice lately because of technological advances that, industry leaders say, can make the water purer than tap water. San Diego and South Florida are also considering or planning to test the idea, and Orange County, Calif., opened a $481 million plant in January, without much community resistance, that is believed to be the world’s largest such facility.

None of the proposals or recycling projects already under way send the treated water directly into taps; most often the water is injected into the ground and gradually filters down into aquifers.

That is what Los Angeles would do, too. But the city abandoned that idea seven years ago in the face of political opposition, and is likely to face some debate about it now.

Fran Reichenbach, a founder of the Beachwood Canyon Neighborhood Association, one of the groups that opposed the plan, said she remained unconvinced the water would be safe.

“I appreciate them trying to save us in a time of water shortage, but the fact remains the kind of toxins and chemicals that are created on daily basis cannot be tested for,” Ms. Reichenbach said, disputing industry claims to the contrary. She said the group would push for independent testing and analysis of the treated water.

But Mr. Villaraigosa and H. David Nahai, the general manager of the Department of Water and Power, said they would push forward.

It will cost about $1 billion to retool the water works to treat the sewage, capture more rainfall and make other improvements. The money, city officials said, will come in part from state grants and fees on polluters, though they have not ruled out increases in water bills as well. The City Council must approve some of the changes.