Premier Dominic Perrottet says NSW will go it alone if the federal government refuses to split the cost of raising the Warragamba Dam wall.
The project was designated as critical state significant infrastructure earlier this month to cut red tape, but NSW is yet to secure a funding commitment from Canberra.
"This is a project that is going to happen. We are raising the Warragamba Dam wall," Mr Perrottet told reporters at a State Emergency Service centre in Sydney on Tuesday.
"The reason this needs to occur ... is that in a catastrophic event we would have 75,000 people required to be evacuated from western Sydney.
"Raising the Warragamba Dam wall is the only solution as it protects downstream communities in times of flood but also protects Sydney's drinking water in times of drought."
Reports from Water NSW and an environmental impact statement would be completed "as soon as possible".
The premier would not be drawn on whether these reports and the business case for federal funding would be finished by the March election.
Mr Perrottet dismissed comments by Treasurer Matt Kean that the $1.6 billion, four-year project to raise the wall by 14 metres was economically unviable without crucial federal funding.
"You can't put a price on human life and ultimately this is a project that I would expect the commonwealth government to provide 50-50 funding for," he said.
However, later on Tuesday Mr Kean backed the premier saying "if we have to go it alone, we will", adding it will be funded "in a financially responsible way".
But Labor's Water spokeswoman Rose Jackson raised concerns about how the project would go ahead, without it being accounted for in the budget.
"The people of western Sydney and Hawkesbury-Nepean Valley need real answers right now," she told reporters.
"There's no funding for the project, there's no timeline for the project, there's no timeline for the EIS (environmental impact statement)."
The premier's vow to proceed with or without federal funding was "a desperate political act months before the election" exhibiting "political immaturity", she said.
She also questioned the effectiveness of the project, saying about 45 per cent of flood waters in that part of western Sydney came from catchments that were upstream from Warragamba.
She urged Mr Perrottet to call Prime Minister Anthony Albanese to show how "serious" he was about pushing the project.
Last week, the prime minister insisted that Mr Perrottet had not raised the funding directly with him.
"This is all about protecting lives. We need to get on with it," Mr Perrottet said.
