Los Angeles mayor Eric Garcetti Tuesday joined descendants of the engineers who brought water to the then sleepy Californian town, marking the 100th anniversary of the transformative project.

Actors helped re-enact the moment when the Los Angeles Aqueduct gates were first opened in Sylmar, in the mountains north of the now sprawling West Coast metropolis.

"There it is, take it!" proclaimed an actor playing engineer William Mulholland, whose words announcing the arrival of life-giving water in the LA basin on November 5, 1913 are part of the city's lore.

Water gushed towards the city along the 233-mile Los Angeles Aqueduct, which transports water from the Owens Valley to Los Angeles.

The aqueduct brought "water that truly created the city of Los Angeles, without which we would not be sitting here today," said Department of Water and Power chief Ron Nichols.

Guests at the ceremony included Christine Mulholland, great granddaughter of the chief engineer, who also gave his name to celebrity home-lined Mulholland Drive, which winds along the ridge of the Santa Monica Mountains and Hollywood Hills north of LA.

Los Angeles' population expanded from about 300,000 to 800,000 in the decade after the aqueduct opened.

"Think about that. In a decade, half a million people moving her because of what this aqueduct was able to do," said Garcetti. "Today we're a global capital of 4 million and a metropolitan region of 12 million."

That huge population makes ever increasing demands for water, a constant challenge in southern California, which enjoys 300 days of sunshine a year.

"After years of taking our water for granted, something radical again must be done," said the LA mayor. "There are no more sources to tap. There are no more pipelines to build. Los Angeles can, must and will protect its destiny."

And he added: "So, as we might have said in the past, 'Here it is, take it,' I say to you today: here it still is .. .let us treasure it, let us conserve it, let us share it."