The Hunter Valley Research Foundation survey, commissioned by the Newcastle Herald, showed 21 per cent of surveyed residents disagreed with the dam's building and another 20 per cent were strongly against the proposal.

It follows a Roy Morgan Research survey in December, which showed less than one in four Hunter residents surveyed about the proposed dam supported its construction.

The latest survey indicated the Tillegra debate had fallen on most ears, with more than eight in 10 respondents aware of the project at some level.

Only 6.2 per cent strongly backed the dam and 15.8 per cent agreed it should go ahead.

Greens MP John Kaye said the results were evidence "public relations spin" from Hunter Water had failed to hide the reality of an "unnecessary, expensive and damaging" dam.

"Hunter Water has failed to hoodwink the community," he said.

"Almost twice as many people have seen through the utility's propaganda as have fallen for the myth that the Hunter needs a new dam."

Dr Kaye said a decision to push ahead with the project despite support from less than a quarter of residents would cost political seats in the Hunter.

No Tillegra Dam Group chairwoman Carol Pasenow said the community had never truly believed that the dam was justified or needed.

Hunter Water would not comment on the survey and released a statement saying it had a responsibility to provide clean, safe drinking water for the Hunter population.

The survey involved telephone interviews with 310 Hunter residents.