Councillors voted in favour of undertaking the feasibility and investigation works at the council's February meeting.

The plant was included as part of a host of measures to address water security, outlined in council's Water Supply Security Update report.

Planning and investigations for the report started in December 2019, to ensure council can continue to deliver water to the community through the unprecedented intense drought period.

Due to the short-term risks and current situation regarding water storage levels and predicted rainfall, the report outlined some projects which are underway to ensure a secure water supply.

The projects included a seawater reverse osmosis desalination plant, in-dam water treatment, upgrade of the Wauchope Treatment Plant and recycled water to supplement the drinking water supply.

At the council meeting, Mayor Peta Pinson raised the issue of cost and questioned how expensive the initial investigation and planning for a desalination plant would be.

Council's general manager Craig Swift-McNair said the initial investigation and planning would cost about $500,000.

According to the report, further detailed designs and environmental approvals for desalination plant costs would be in the order of $3 million.

This was in comparison to the proposed Belmont (south of Newcastle) 15ML/day temporary desalination plant, where the capital costs required are in the order of $90 million.

Last year MidCoast Council also fast-tracked the development of a temporary desalination plant near Nabiac to supply emergency water, in case it was required in 2020.

The project was halted in January this year, when widespread rainfall meant the plant would not be needed.

According to MidCoast Council's Director Infrastructure and Engineering Services, Rob Scott, a desalination plant is an expensive option, especially if it's temporary in nature.

The overall cost of the Nabiac project, including running the desalination plant for six months, is estimated to be more than $12 million.

Mr Scott said MidCoast Council committed to a desalination plant to mitigate the need to go to level five water restrictions.

"In effect it was an insurance policy against harsher restrictions which would have damaged the economy," he said.

Mr Scott said without the additional security for the water supply, the economic impact of harsher restrictions would have been much more than the cost of the desalination.

"If harsher water restrictions only impacted a quarter of businesses by one per cent, then our economy would lose more than $8 million dollars," he said.

"In reality, water restrictions impact a larger number of businesses by much more than one per cent."

In the longer term, MidCoast Council has other options that are not as expensive as desalination.

"When we went with the temporary desalination plant last year, time was the main factor that drove this decision," Mr Scott said.

The Nabiac plant was expected to produce 5.5 million litres of water per day. The water will be desalinated through a reverse osmosis process in temporary desalination units, that are connected to the Nabiac Water Treatment Plant at the Nabiac Borefield.

Mr Scott said council also maximised the ability to produce water from the Nabiac Borefield as a priority over the desalination project.

"This is permanent and we can continue to use it in the future," he said.

"We had planned to do that work in the future and it made sense to bring the timing forward."

Similarly, Port Macquarie-Hastings Council is also planning to upgrade the Wauchope Water Treatment Plant.

The intent of the large bulk water treatment plant is to allow more water to be extracted from the river during periods of high flow, which increases the overall yield and thus security of the supply system in the long term.

Investigations and the initial planning works for a proposed desalination plant within the Port Macquarie-Hastings are set to be completed in 2020.

This is so construction works can be fast tracked in 2021, should the plant be required.

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