A 700-litre flood of water that forced a Qantas plane to turn back to Los Angeles mid-flight may have been caused by the mops used to clean the aircraft.
An investigation into the "lakes on a plane" incident on QF94 has found the crew were advised that there was no immediate concern for safety when a water pipe burst shortly after it departed for Melbourne on July 2.
The water had leaked from a loose pipe coupling in the business class galley and a small amount of water also leaked from the same coupling on a replacement aircraft when it was inspected before take-off the following day.
Subsequent inspections found rope-style mops used by cleaners may have contributed to the coupling that joined the water pipe coming undone.
Strands of the mops were found tangled in brackets, the Air Safety Transport Bureau investigation found.
"There was evidence that the rope-style mops used by cleaners may have contributed to the coupling coming undone," its report released on Wednesday said.
Fuel was jettisoned as the Airbus A380 made its approach to Los Angeles, reducing the overall landing weight to 445 tonnes, but the plane still came in "above the maximum landing weight of 391 tonnes".
"The flight crew then prepared to conduct an overweight landing," the ATSB said.
Civil Aviation Safety Authority regulations allow for overweight landings in "non-normal situations".
"As the aircraft commenced descent, a cabin crew member advised the flight crew that the leaked water was moving forwards in the aircraft. The flight crew then conducted a slow speed descent to keep the water stabilised and prevent it flowing forwards," the ATSB said.
The aircraft landed without further incident.
An indicator panel showed about 40 per cent of the plane's potable water remained and "about 700L of water had leaked into the cabin".
A fleet-wide inspection of all Qantas A380 aircraft was carried out and preventative action taken on all similar galley installations, including introducing sponge style mops in an effort to prevent similar incidents.
The aircraft manufacturer is working on providing a permanent solution.
But the ATSB also said ground staff contacted as the drama unfolded had advised the water would drain towards the bilges and away from the aircraft's main electronic systems located at the front of the plane, and there was "no immediate concern for the safety of the aircraft".
"The crew did not receive any electronic centralised aircraft monitor indications or warnings."
The 14-hour flight was aborted after it was decided that it was "untenable" to continue as no water was available for toilets or basins.
"Leakage of that quantity of water had not occurred previously and the eventual impact of the water on the aircraft was unknown."
The ATSB praised the actions of the crew aboard QF 94, saying the incident was "an excellent example of effective crew resource management techniques" when faced with an abnormal and unusual situation.