A CSIRO study has found testing wastewater on flights is an effective and cheap way to screen incoming overseas passengers for COVID-19.

Analysing wastewater samples from long-haul flights of returning Australians could be the key to detecting COVID-19 earlier - before passengers show any symptoms.

A CSIRO study of wastewater from Australian repatriation flights returning from hot spots is the first time researchers have matched the plane wastewater testing with follow-up clinical data studies of passengers in quarantine.

The world-leading research could provide a convenient and cost-effective way to detect and manage the importation of the virus and help improve confidence as Australia reopens to the world.

Qantas is starting international flights to and from NSW from November after Premier Dominic Perrottet on Friday announced the scrapping of hotel quarantine for fully vaccinated international arrivals from next month.

CSIRO lead author Dr Warish Ahmed said as global travel returns, wastewater testing of flights can be an effective way to screen incoming passengers for COVID-19 at points of entry.

"It provides an extra layer of data, if there is a possible lag in viral detection in deep nasal and throat samples and if passengers are yet to show symptoms," Dr Ahmed said.

"The rapid on-site surveillance of wastewater at points of entry may be effective for detecting and monitoring other infectious agents that are circulating globally and provide alert to future pandemics."

Author Jochen Mueller from University of Queensland said wastewater testing could be a useful additional tool to stem the spread of the virus.

"Wastewater surveillance from large transport vessels with their own sanitation systems significantly improves our ability to control the spread of infection from overseas travellers," Prof Mueller said.

The samples were taken from toilets of 37 Australian government repatriation flights from COVID-hotspots including India, France, UK, South Africa, Canada and Germany landing at Darwin International Airport between December 2020 and March.

The research found wastewater samples from 24 of the 37 repatriation flights - 65 per cent - showed a positive signal for the virus that causes COVID-19 despite all passengers, except children under age five, testing negative to the virus 48 hours before boarding.

Infected people shed the virus in their faeces about two to five days before showing symptoms.

During 14 days of mandatory quarantine after arriving in Australia, clinical tests identified only 112 cases of COVID-19 among the 6570 passengers - 1.7 per cent.

There was an 87.5 per cent match between the positive detections by surveillance of the wastewater and the subsequent clinical detections made during the passengers' quarantine.