The NSW government will on Wednesday introduce temporary legislation for water infrastructure projects where there is a critical town water supply need.

The Water Supply Critical Needs Bill is designed to secure a town's short-term water supply, and will also fast-track three dam projects.

A $650 million upgrade of Wyangala Dam in the NSW Central West, a $480 million new Dungowan Dam near Tamworth and the Border Rivers project on the Mole River will be completed in faster time frames under the new legislation.

"We don't have months ahead of us for some of these towns, the approval process for emergency infrastructure needs to be made in a timely manner so we do not run out of water," Deputy Premier and Minister for Regional NSW John Barilaro told reporters in Sydney.

Under the legislation, the three dam projects will be treated as critical state infrastructure projects, giving them a timeline.

"Projects like WestConnex saw its approval process delivered under six months. We believe that the same process should apply to these three dams so we can get on with getting bulldozers in the ground next year," Mr Barilaro said on Wednesday.

"The lesson from this drought has to be one about building storage for the future."

Prime Minister Scott Morrison and Premier Gladys Berejiklian on Sunday committed $1 billion to NSW dams and water infrastructure projects.

Ms Berejiklian denied the government is circumventing environmental protection processes by fast-tracking the project.

Water Minister Melinda Pavey said the dams would still go through "very thorough and critical environmental impact statements".

The legislation was aimed at "truncating" the environmental processes the way the Sydney light rail and Sydney Metro projects were, she said.

The legislation will be in effect for two years and can only be extended for up to 12 months where towns experience ongoing severe drought risks.

The Greens water spokesperson Cate Faehrmann accused the government of trying to stop scrutiny of its dam proposals.

"Emergency measures are needed to ensure towns don't reach day zero, but fast tracking the approval of dams that won't be built for another four or five years is a cynical attempt to take advantage of the drought to get away with environmental vandalism," said Ms Faehrmann, Greens MP and water spokesperson.

"Building more dams won't make it rain but they will consign downstream communities to environmental and social disaster as even more rivers dry up."

Australian Associated Press