The main broke on the 1100 block of North Formosa Avenue near Santa Monica Boulevard at about 11:30 p.m. Wednesday.
It was unknown what may have caused it to break.
The busted main gushed out about 30,000 gallons of water, rising up to 6 feet in the parking garage, causing cars to float.
About 30 customers were without water service in the area.
"I noticed I didn't have water in my house, so I called LADWP and they didn't know what was going on, so I came out to my porch," said resident Ricky Bansal.
At least six cars were in the garage at the time of the incident. L.A. County Fire Capt. Rick Brandelli said a Porsche, a brand new Volkswagen, several compact cars and an SUV were impacted from the incident.
"The cars were all submerged. I could not see any cars. I could not believe there were any cars inside, to be honest," said Bansal.
Crews with the Los Angeles Department of Water and Power worked through the night to pump the water out of the garage and into the streets.
"Right now, they're just doing the cleanup. We've already restored the water and now we're getting ready to restore the street," said Ben Gook with the LADWP. "There is a 20-by-30 foot patch in the street that needs to be repaired."
Despite all the damage to personal property and the streets, residents say they're thankful everyone is OK.
"Things can be replaced, you know, life can't. As long as no one was injured, after the shock wears off, I think everyone will be fine," said area resident Tod Hallman.
Water service has since been completely restored.