A spokeswoman for the Australian airline confirmed the flight, QF 94, had returned to Los Angeles International Airport yesterday about an hour after takeoff because of leaking water on the upper deck of the plane.
Qantas said there were no safety concerns for passengers on-board. However, it did not release the number of passengers on board the plane that can carry over 500 people.
Video from Australia's Channel Seven Network showed water running down the aisle of the plane.
The water made its way through the floor and showered economy-class passengers below, the network reported.
Crew members moved passengers and gave them blankets to stay dry, the airline said in a statement.
"Crew on board did everything they could to help customers, including moving them to unaffected areas and providing spare blankets so they could stay dry," a spokeswoman said.
"There were no safety of flight concerns with the water leak, however the Captain decided to return to LA in the interests of passenger comfort."
The leaked water was drinking water kept in pipes on- board, the spokeswoman said.
In a statement on the airlines website, Qantas apologised to customers and stressed there were no safety of flight concerns with the water leak.
"We are liaising with Airbus to understand what caused this fault," Qantas said.
Some reports on Twitter suggested the water soaked through the roof into economy section of the plane.
Passengers took to social media to share photos of the waterlogged cabin.
"Pipe burst on my #Qantas flight over the Pacific. We were diverted back to LA. River running through the aisles," Yvette Nicole Brown, an American actress who stars in the TV sitcom Community tweeted.
Another passenger tweeted pictures of the wet plane, posting photos of the water-soaked seats and isles.
The mishap follows another incident in April, when another Los Angeles-Melbourne flight involving an A380 Airbus was turned back due to a fuel pump fault.
The Airbus A380 is the world's only complete double- decker airplane. It has a capacity to carry 525 passengers in a comfortable three-class configuration, and up to 853 in a single-class configuration.