Video and photos taken by passengers show water running down the aisles and seeping from the business class cabin floor down into the economy cabin below.
"It look liked a trickle at first and I thought someone had spilt a soda or pop or something and it just got bigger and bigger and it filled up both aisles," Brown told CNN.
"It literally was like a river running down the aisles of the plane. It was the scariest thing I have ever seen."
Brown feared the plane could short out or passengers could be hurt.
"It seemed like a problem to me because it is water and electricity," she said.
"All I kept thinking about was, 'We are over the Pacific and I'm in something that is full of electricity and there is water'.
BREAKING PHOTO: Qantas flight forced back to LA after water SOAKED THROUGH ROOF into economy @7NewsBrisbane pic.twitter.com/wgZOz2kC2i
"The other thing was it was a double decker plane so I was wondering where the water was going because it flowed by us.
"But I'm thinking 'there's people below us'. There's a staircase behind us and sure enough it became a downpour for them."
Some passengers took to social media to share photos and their fears of being deluged, while others joked the incident should be made into a film titled "Lakes on a Plane".
Qantas said the leak was from drinking water. A spokesperson said there were no safety concerns and the captain made the decision to turn back to LA.
The plane took off from LA International Airport just after midnight on Wednesday, LA time, and landed back in LA at 2.39am.
Passengers were taken to hotels and, according to the Qantas website, the flight was scheduled to take off at 8pm Wednesday LA time and land in Melbourne on Friday at 4.50am AEST.
"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," Qantas said in a statement.
"We're also providing customers with hotel accommodation while the issue is being fixed by our engineers in Los Angeles. We apologise to customers for the inconvenience.
"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. We are liaising with Airbus to understand what caused this fault."
Brown, although scared, was full of praise for Qantas flight and gate crews, describing them as "awesome".
Earlier, she wrote to her 469,000 Twitter followers: "Pipe burst on my #Qantas flight over the Pacific.
"We were diverted back to LA.
"River running thru the aisles #ScaryTimes #WillKeepYouPosted.
"Man! It was a RIVER in the plane down BOTH aisles.
"And we were the lucky ones.
"It rained on those below."
- AAP
