A Qantas flight from Los Angeles to Melbourne was turned back about an hour into the 14-hour flight after water started gushing down the aisle into economy from a leaking pipe in business class.
A spokeswoman for the airline said the captain decided to return the A380 to Los Angeles due to passenger discomfort, rather than any fears about safety.
The water came from the plane's drinking water supply, she said.
It leaked into the economy cabin through the roof, from the business class cabin on the upper deck.
"It wasn't a safety issue, it was just passenger discomfort," the spokeswoman said.
''It was an inconvenience for passengers. Crew did everything they could by moving passengers to unaffected areas and giving them extra blankets.''
She confirmed the flight had been returned to Los Angeles. She said engineers were assessing the leak and whether it could be repaired or if another aircraft would be needed to fly to Melbourne.
After contacting Sydney headquarters for advice from engineers, Fairfax Media understands the crew was told to turn the plane back.
One passenger who contacted Fairfax Media said he understood the leak started in the water supply pipes at the rear of business class on the upper deck. The water then flowed down, landing on up to 80 passengers sitting in economy.
The passenger, who wanted to remain anonymous, said Qantas staff handled the situation professionally and passengers were largely understanding.
''It's just like the weather, there's no point worrying about it because you can't do anything about it,'' he said.
Passengers on board the flight, which departed about 11pm Tuesday local time, were being put up in hotels overnight while the plane was assessed by engineers, the spokeswoman said.
The plane returned to Los Angeles at about 2.30am on Wednesday morning, local time. Passengers are expected to depart Los Angeles at 8pm on Wednesday.
Flight QF94, an A380 Airbus, had left Los Angeles Airport on time at 11.30pm on Monday night.
News of the leaking pipe reached Twitter not long after the plane landed back in Los Angeles.
Melbourne man Ken Price was heading home on the flight after a six-week holiday with his partner.
“We were about an hour into the flight and all the passengers in the middle rows, all the middle rows towards the back, started jumping up,” Mr Price told Fairfax Media.
“We just saw all this water just flowing down from the overhead compartments.
“We were right at the back of the plane and the stairs to go up were just a raging torrent of water.”
Mr Price said the plane’s entertainment systems and ovens were turned off, and “survival packs” of food were handed out to passengers.
“Everyone was just standing in the aisle and wondering what was going to happening. It went on for about 45 minutes I’d say before they decided to turn the plane back,” he said.
Mr Price, a hotel owner, said he would have to wait until Wednesday afternoon LA time to get on another flight to Melbourne.
“We’re all getting a bit frustrated now ... it’s time to go home,” he said.
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. Then, a warning light alerted crew to a problem with the fuel pumps approximately 4.5 hours into the flight.
In a statement on the airlines website, Qantas apologised to customers and stressed there were no safety of flight concerns with the water leak.
The airline said it would liaise with Airbus to understand what caused the fault.
- with Patrick Hatch