That's according to Associate Professor of Hydrogeology at the University of NSW Bryce Kelly, who has spent more than a decade studying groundwater in the Central West.

He says current withdrawals "will only be sustainable if the Narromine region gets flooded frequently enough to balance the volume of groundwater extracted."

It's an issue that has seen Central West residents locked in debate over both the NSW government's management of water resources, and the long-term sustainability of intensive agriculture.

A total of 65,375 megalitres of groundwater was allocated last year to 117 license holders in the Lower Macquarie Region stretching from Narromine to Nevertire.

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It eased some of the stress that comes with waiting for rain in an unrelenting drought. It also safeguarded their properties when Burrendong Dam fell below two per cent capacity in late January.

Jon Elder farms cotton just south of Narromine. He hasn't had a surface water allocation in two years and relies solely on a groundwater license to see his 470- hectare property 'Waverleigh' through the dry season.

"Water is the limiting factor in everything we do," he said, speaking just a few months out from harvest. "It's been a really challenging year for us because of how hot and dry it is. Normally you would expect to get a bit of help from above - I'm talking rainfall."

Mr Elder pumps groundwater from a bore pipe that extends 80 metres below the surface into a deep aquifer. The water in this aquifer is estimated to have soaked into the earth tens of thousands of years ago and is sometimes referred to as "fossil water".

Associate Proffessor Kelly says that while there is no risk of it running dry any time soon, there are few opportunities for an aquifer of that depth to replenish its water supply.

"We do not know what the future flood frequency will be, especially given the impacts of climate change on inland NSW," he said.

The warming climate has not only reduced rainfall but increased evaporation of soil moisture. Each time it rains, the water is used to top up the soil water store and rarely soaks deeper into the groundwater.

On top of this, there hasn't been a major flood near Narromine since 2010.

Community members have called into question how the current rates of groundwater extraction will impact sustainability as we head into an uncertain climate future.

Associate Professor Kelly says they should be reassured that when the Water Sharing Plans were devised, "a lot of hard work went into ensuring the current annual rates of withdrawal were sustainable".

However, he emphasises that allocations need to be constantly reviewed.

"You have to pump aquifers for a long time - decades in some places - before you can determine if the extraction is in balance with recharge.

"We are getting better, but it simply takes a long time to see the impacts in these systems."

In the meantime, Jon Elder, like many other irrigators in the region, has put his faith in the government to ensure the region's water supply outlasts predicted future droughts.

"If the science is wrong and if the drought does start to impact the water - and [if] there isn't enough water left to use, we will adjust our usage to that accordingly."