The Victorian Coalition has gone back on its pledge not to take water from the controversial north-south pipeline — while the State Government has suggested 165 litres a day is the maximum people should use.

In an embarrassing U-turn four days after it vowed water would not flow down the pipe, Liberal shadow water spokeswoman Louise Asher yesterday said the $750 million pipeline would be used as an insurance policy for "critical human needs" if the Coalition won power in 2010.

"We have been very upfront that the pipe will not play a role in Melbourne's water supply as a matter of course; it will be there as a last resort," she told The Age.

"There needs to be a transitional … plan until our projects come on line."

But last Thursday, Ms Asher promised a Liberal-National government "will not take water from the pipeline", arguing water could be sourced from new dams, desalination and recycling.

The next day she repeated the promise to turn off the 70-kilometre pipe and said the Coalition "do not believe it is a morally just project".

Water is scheduled to flow through the pipe in 2010.

Last night, Water Minister Tim Holding attacked the policy change, branding it a "humiliating backflip" for Coalition leader Ted Baillieu.

"This is a sneaky trick to say one thing in regional Victoria while saying the opposite to people in Melbourne," he said.

Mr Holding called on Coalition deputy and Nationals leader Peter Ryan to state whether his party endorsed the Coalition commitment to use water savings from the pipe.

Mr Baillieu has not endorsed or commented publicly on the policy not to use the water.

Yesterday, he and his office did not respond when The Age asked via email if he supported Ms Asher's comments that a Liberal-National government would not take water from the north-south pipeline.

Construction on the pipeline from the Goulburn River to the Sugarloaf Reservoir started last week, with 75 billion litres of water expected to be delivered to Melbourne each year from irrigation upgrades in northern Victoria.