South Australian Water Minister David Speirs has taken aim at NSW over its refusal to contribute to 450 gigalitres of environmental flows guaranteed under the Murray-Darling Basin Plan.

"This was an example of fake news at its best from NSW," he told ABC radio on Wednesday.

"Completely different rhetoric was used outside the room in front of the media than within the ministerial council."

NSW Water Minister Melinda Pavey emerged from Tuesday's ministerial meeting hailing major wins and concessions before flatly rejecting to contribute to the 450GL.

"We've made it clear we have no more water to give," she said.

But Mr Speirs claims her tone was very different behind closed doors.

He warned the NSW refusal to chip in for the environmental flows could result in forced federal government buybacks.

"That will have a very unfortunate set of consequences for regional communities," the SA minister said.

But NSW are yet to make good on threats to exit the plan after months of raising the prospect of pulling out.

"If NSW walks away from the 450 gigalitres, they are essentially walking away from the Murray-Darling Basin Plan," Mr Speirs said.

Federal Water Minister David Littleproud argues all states have a legal commitment to delivering an initial 62GL of environmental water.

But Ms Pavey said releasing more environmental water wouldn't meet the social, economic and environmental neutrality test agreed to last year.

Acting Prime Minister Michael McCormack said the water could not be delivered from NSW without meeting the test.

"That water will never be delivered if it's going to have a social and economic downturn for those communities which rely on river water, which rely on irrigated water," the Nationals leader told Sky News on Wednesday.

Mr Littleproud is adamant the remaining 20 per cent of the plan can be achieved through water infrastructure projects rather than buybacks.

"No one wants to go near buybacks and that's why it takes leadership not politics," he said after the ministerial meeting.

Labor has criticised the federal government for not passing laws to make interim basin inspector-general Mick Keelty's role permanent.

"The Murray-Darling Basin requires national leadership; instead the Morrison government is using the states as a scapegoat for its failures," opposition frontbencher Mark Butler said.

Mr Littleproud said legislation would be drafted and urged states to support the inspector-general after some raised concerns with the proposal.

Australian Associated Press