Twenty per cent of annual rainfall can potentially result in the harvesting of a gigalitre of storm water, reports Dubbo's water for the future coordinator Chris Devitt.
The consultant and Dubbo Regional Council's former infrastructure and operations director says "five millimetres of rain can make the pipes run".
Storm water harvesting is a key component of Dubbo Regional Council's water security strategy, prompted by the drought and the prospect of Burrendong Dam running out of water by mid-2020.
The council's chief executive officer Michael McMahon reported to its September meeting of detailed concept planning of the first stages of a storm water harvesting scheme.
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Currently, underground drainage pipes discharge storm water along the Macquarie River or to Eulomogo Creek.
Mr Devitt, who has worked on a storm water harvesting project in Orange, says Dubbo has what it takes to capture "quite a reliable source of water".
..five millimetres of rain can make the pipes run.Dubbo's water for the future coordinator Chris Devitt
"You will always get some run-off after a storm on an urban catchment because of the impervious surfaces," he said in reference to the likes of roads, footpaths and roofs.
Mr Devitt said by building a "structure at the outlet of a pipe", a portion of storm water could be captured and put through a "fairly simple treatment process" before entering the John Gilbert Water Treatment Plant.
In his report to the September meeting, Mr McMahon said the harvested storm water along with "raw water" from the river and/or groundwater would be fully treated to the appropriate Australian drinking water standards before being distributed for general use.
"Water quality data from similar schemes in NSW demonstrate that the quality of harvested storm water is generally significantly better than that of raw water from natural sources such as creeks and rivers," he said.
"This is due to the fact that with a whole-of-catchment management approach the potential for contaminants to enter storm water is limited, and the initial pretreatment process can be designed to address any potential contamination issues which would occur within the catchment."
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Mr McMahon said storm water was "effectively a new source of water" which could be readily incorporated into the city's water supply "without significant impact on other users".
It was both a short-term and long-term solution to the city's water crisis and offered a "very cost-effective option which delivers significant long-term environmental outcomes", he said.