The Murray-Darling Basin Royal Commission has accused the SA Government of surrendering to the Federal Government and has suggested the state's Water Minister David Speirs breached ministerial code.

Key points: A deal with upstream states was "totally antipathetic" to SA interests

A deal with upstream states was "totally antipathetic" to SA interests The commissioner said Mr Speirs "almost certainly" breached his code of conduct

The commissioner said Mr Speirs "almost certainly" breached his code of conduct Mr Speirs said he was disappointed by that commentary

Commissioner Bret Walker SC's scathing commentary related to a ministerial meeting in December, where South Australia joined with other states to agree to terms on how environmental water would be returned to rivers.

The meeting agreed to return up to 450 gigalitres (GL) of water to the environment, provided it did not have a negative socio-economic impact on river communities, based on criteria agreed to by the states.

In return, South Australia received $70 million of funding from the Federal Government to spend on rehabilitating the struggling Coorong wetlands.

However, in his report Mr Walker found the decision to support the agreement was against the state's interests.

"It is nothing short of a capitulation to the interests of the current Commonwealth Government, and those of Victoria and New South Wales," he said.

"It is so contrary to the interests of South Australians that the decision by the Minister responsible is almost certainly a breach of at least [clause] 2.5 of the South Australian Ministerial Code of Conduct.

"No minister acting reasonably could consider these changes to the criteria to be anything but totally antipathetic to the interests of South Australia, and the South Australian environment."

That section of the code states that ministers should not make official decisions without considering the "impact the decision is likely to have" on the interests of the "citizens of South Australia".

SA Premier Steven Marshall said he did "not accept" the royal commissioner's criticisms.

"I think that the Minister has done an excellent job negotiating with the Commonwealth," he said.

"We've been in Government for 10 months. We've been able to secure more money to [come] into South Australia to support the Coorong."

Mr Speirs said he was disappointed with the commentary in the report.

"It is an isolated comment that doesn't consider all the other things that occurred, that we did get New South Wales and Victoria to the table for the first time in history, that we did get 450 GL of water," he said.

"We did get $70 million for the Coorong that concerns South Australians so much.

"The ministerial council in December was incredibly successful for South Australia and it got that pathway forward."

Desalination plant would have 'little impact'

The 746-page report of the Murray-Darling Basin Royal Commission. ( ABC News )

The royal commission report also questioned the State Government's decision to agree to investigate whether the Adelaide Desalination Plant could be used to offset water diversions elsewhere.

"Why the South Australian Minister agreed to this proposal is not clear," Mr Walker said.

"This is particularly concerning, given that the relevant South Australian department received a comprehensive, independent cost-benefit analysis in June 2016, that determined the desalination plant should only be used when temporary water market prices reach a critical pricepoint, namely above $510 per megalitre.

"On that analysis, it should therefore not be used as a permanent 'support' to annual water recovery targets.

"Either the Minister was unaware of this report, has determined it is deficient in some way or has simply chosen to ignore its existence.

"All of these scenarios are concerning."

Mr Walker said Adelaide's urban water usage represented about 1.25 per cent of basin-wide diversions.

"Running a desalination plant for Adelaide's metropolitan water usage, therefore, could have little impact on upstream diversions."

Report raises 'extraordinary questions' for Premier

The SA Government has not ruled out water buybacks as a solution. ( ABC Open contributor mickw78 )

The Murray-Darling Basin Royal Commission was announced by the previous state Labor government in 2017.

Labor leader Peter Malinasukas said today said the accusation that Mr Speirs had breached the ministerial code of conduct was "nothing short of extraordinary" and put Premier Steven Marshall "front and centre about what sort of Government he is going to lead".

"David Speirs went over to Canberra, politely agreed with everybody in a way that was fundamentally contrary to the interests of South Australia, that is not standing up for our state," he said.

Mr Malinauskas stopped short of demanding Mr Speirs be sacked, but said Mr Marshall should "do what he promised he'd do and that is hold his ministers to account".

"Every South Australian can remember how hard we all fought for that extra 450 GL and then within months of coming into office they've sold it away," he said.

"They've agreed to things that almost certainly ensure that we'll never have that water delivered, that is genuinely heartbreaking."

Mr Speirs said it remained "absolutely critical" that the 450 GL was secured for the environment, and there was Federal Government money which did "enable buybacks to occur potentially in the future".

"However, there are many regional communities concerned about buybacks because they have a particular economic and social impact," he said.

'Colloquial terms' used at notorious restaurant meeting

The royal commission also shed light on the infamous exchange between former South Australian water minister Ian Hunter and his federal and state counterparts in November 2016.

Ian Hunter told Barnaby Joyce to "leave his jurisdiction". ( Carl Curtain )

At the time, it was reported that Mr Hunter repeatedly said "f*** you" to Victoria's Water Minister Lisa Neville and called her a "c***" before storming out of the dinner at Adelaide's Rigoni's restaurant.

He also reportedly told the gathering, which included then federal water resource minister Barnaby Joyce, "f*** you all".

Mr Hunter later denied using "some particularly inappropriate words", but admitted to using "inappropriate language" and issued an apology.

The royal commission report stated that a "hard conversation" took place at the restaurant.

"The South Australian minister made his, perhaps the then state government's views, known to his interstate and Commonwealth colleagues in unambiguous terms, with Minister Hunter apparently telling Minister Joyce, in colloquial terms, to leave his jurisdiction."