State and territory water ministers unanimously agreed to the appointment of a new Murray-Darling Basin Inspector-General following a meeting on Sunday.

The idea was put forward by federal Water Resources Minister David Littleproud who said the independent umpire would have the power to investigate suspected water theft, as well as ensure that efficiency and recovery projects are delivered across the river system.

The position wouldn't replace the Murray-Darling Basin Authority, however, it will hold the regulator to account, along with the federal and state governments.

"The inspector-general will be a tough, but fair cop to oversee all state and federal agencies delivering the Basin Plan," Mr Littleproud said on Sunday.

"They will make sure all agencies live up to their responsibilities and can investigate allegations of water theft."

The inspector-general will also report back to the Murray-Darling Ministerial Council every six months and appear at Senate estimate hearings.

"The good will taken to create this position reassures me that this new role will help to rebuild trust between the states," Mr Littleproud said.

"It will also give basin communities greater confidence the plan is being rolled out fairly.

"This is the best plan we have, and we all need to work together to deliver it."

Northern Basin Commissioner and former federal police commissioner Mick Keelty will become the interim inspector-general until federal parliament passes legislation to create the role.

The new role is expected to be established by 2020 and have powers under the Water Act 2007.

Ahead of the meeting, NSW and SA were at loggerheads over 450 gigalitres of water designated as environmental water in the southern basin.

NSW's water minister Melinda Pavey said the long-running plan may not be achievable, sparking a firm response from her SA counterpart David Spiers.

"Whilst the plan is not perfect, it is the only plan we have got, and for it not to be delivered would be the worst result for South Australians and the basin as a whole," he said in a statement.

"We now have the plan back on track and with state and federal elections out of the way, we have some clear space to see real action to improve the overall health of the river system."

Ms Pavey after the meeting slammed the federal and South Australian governments for refusing to back an independent review of the plan's target.

She said NSW and Victoria would therefore jointly conduct their own review to examine "what can actually be achieved".

NSW deputy premier John Barilaro said Sunday's meeting was an opportunity to deliver "real certainty".

"Instead, we got served up the threat of more water buybacks from the commonwealth and South Australia refusing an independent review," the Nationals leader said in a statement.

The Murray-Darling Basin covers about a seventh of Australia and provides for 40 per cent of agricultural production.

Australian Associated Press