Dubbo's water for the future coordinator Chris Devitt calculates that the city will have water past Christmas 2020 based on a worst-case scenario of the Macquarie River ceasing to flow next May and Dubbo Regional Council not being able to buy more groundwater.
Dubbo's water crisis is the result of a drought that is not like its predecessors and a forecast of "no rain in sight" for the next six months, he says.
The council has a multifaceted plan to keep water flowing through taps into the future including water restrictions, the construction of a pipeline to move effluent into the city to free up groundwater being used to irrigate recreational areas, and buying more groundwater.
Mr Devitt says the city needs 6.5 gigalitres (GL) of water in a year of level four water restrictions.
The council is looking to boost its groundwater use from 2GL to its annual entitlement of about 4.3GL from the Upper Macquarie alluvial aquifer.
It is set to launch an expression-of-interest process to buy about 2.2 GL of groundwater to meet the 6.5GL target.
If we only got our entitlement that would keep us going probably until January or February 2021.Dubbo's water for the future coordinator Chris Devitt
Mr Devitt said the transfer of water from Windamere Dam to Burrendong Dam, and the pumping of its remnant storage water, would keep water flowing down the Macquarie River to Dubbo until May in the absence of rain.
"That doesn't mean everything stops because we've still got our groundwater entitlement which will keep the city going pretty much to the end of next year," he said.
Mr Devitt said the city had enough river water and groundwater "to get us to the the end of this financial year", which also marks the end of the water year.
"The river will run till May and two months in winter time is not a big extra demand so we will still have plenty of groundwater entitlement to get there," he said.
The consultant said the annual entitlement would kick in on July 1 when the new river year began.
"If we only got our entitlement that would keep us going probably until January or February 2021," he said.
"It would not get us through a full year because we need 6.5GL but it will get us past Christmas."
Mr Devitt said by 2021 the council would have "probably bought more water entitlements".
"There's a lot of things we've got in train," he said.
"There's time to do them but we can't muck around."
The worst drought in the history of NSW has resulted in a "third fill season" where rain has not replenished Burrendong Dam.
"I think that's the first time that's been the case," Mr Devitt said.
"I guess the other thing is predictions of no rain in sight for the next six months.
"That's why there's been more concern this time than there has in the past."
The consultant said the dam's catchment was "so parched that it's going to take a lot of rain to make it run".