During a press conference with senators from across the political spectrum this morning – without, conspicuously, the Liberals – Premier Jay Weatherill defended SA Environment Minister Ian Hunter’s call for an open judicial inquiry into allegations, aired on last week’s Four Corners program, that senior New South Wales public servants had colluded to subvert the national water agreement and abet “water theft”.

The report claimed that huge volumes of water purchased by the taxpayer as part of the Murray-Darling plan’s environmental measures were instead being diverted to some NSW cotton-growing operations, and suggested senior NSW public servants turned their back on internal calls for investigations into illegal pumping from the river system.

Hunter told ABC Radio Adelaide earlier this morning that that judicial inquiry should be held in public – and also that it should be up to the “eminent jurist” appointed to decide which elements are considered in secret.

“At the very least, the proceedings should be made public just to restore the confidence of Queenslanders, Victorians, South Australians, Canberrans, and hopefully New South Welsh people as well, because this goes to the heart of an agreement … to return the River Murray to health,” said Hunter.

He added that the openness of such an inquiry would “be a matter for the jurist who is appointed as a judicial lead … you would leave that in the hands of the eminent jurist who’s going to be appointed”.

“They will have the experience to make these inquiries.”

The approach stands in contrast to the State Government’s approach to ICAC inquiries into potential maladministration by South Australian government employees.

Last month, the Government voted down a bill that would have allowed SA Independent Commissioner Against Corruption Bruce Lander – an eminent jurist – to hold public hearings into potential maladministration if he so chooses.

Lander had argued he needed the power to hold open hearings, at his discretion, to maintain public confidence in the “integrity” of his investigation into the Oakden Older Persons’ Mental Health Service scandal.

He has never argued for public hearings into corruption allegations – only those that considered maladministration.

Asked why the Government continued to deny Lander powers to hold public inquiries into maladministration, yet advocated giving a jurist the power to hold a public inquiry into allegations from the Four Corners program – which are described in the Senate motion to establish the judicial inquiry as “allegations of theft and corruption” – Weatherill told reporters this morning: “It’s just a separate matter that has different considerations”.

He said the New South Wales ICAC system, which holds open hearings into allegations of corruption, had unfairly stained reputations.

The Senate motion, to be moved by SA Labor Senator Penny Wong, asks the Upper House to express “deep concerns over allegations of theft and corruption in management of water resources in the Barwon-Darling Basin raised by the Four Corners report on Monday 24 July 2017”.

But Weatherill denied that public hearings for the judicial inquiry he was advocating would have the same potential impact on reputations as open ICAC corruption hearings.

“Our experience of the New South Wales ICAC system is that the mere allegations that have been made against somebody … can stain reputations, in a way which is incapable of being retrieved,” Weatherill said.

“What we’re talking about here is a judicial inquiry – the judicial officer in question could choose to deal with it in precisely whatever way they saw fit.

He stressed that Lander’s inquiry into the Oakden scandal would make his final report public.

At the time of announcing his investigation, Lander said his preference was to make the final report public, but would have to consider the issue once it is complete.

SA Opposition water spokesperson David Spiers told InDaily this morning the State Government wanted “one rule for the Labor Government in South Australia and another … for the rest of the world”.

“It’s incredibly hypocritical,” he said.

“Our (SA ICAC) hearings should be held in public.”

Speirs added he was disappointed the Liberal Party was not invited to be part of this morning’s press conference, despite expressing support for a judicial inquiry last week.

“For them to shut the State Liberal Party out shows … they are purely playing politics with this issue,” said Speirs.

“If invited to be part of it, I’m sure we would have.

“We would (taken) have a bipartisan approach.”

Asked why the Liberal Party had been excluded, Weatherill had told reporters this morning that “the Liberal Party are the problem at the moment”.

“We’ve brought together a broad cross-section of senators.

“If there are other senators that wish to join this push I’m sure we would welcome their involvement.”

He said the Labor Party, the Australian Conservatives, the Greens, and the Nick Xenophon Team were “all seeking to advance the same interest”.

The group was gathered to deliver a joint statement that reads: “We as South Australians stand together in solidarity for our River Murray and in support of the Murray-Darling Basin Plan.”

“We call on Prime Minister Malcolm Turnbull to commission a fully independent judicial inquiry into the allegations raised on Four Corners in order to be sure that the Basin Plan is not undermined, and will continue to deliver our share of water to South Australia.”

Turnbull yesterday ordered the Murray Darling Basin Authority to review its compliance measures for the plan.

But Xenophon told the conference that was “like Caesar judging Caesar”.

“It’s unfair to require the MDBA to effectively investigate itself … along with all of the other bodies involved,” he said.

Xenophon last month said his SA Best party was considering running candidates against Trade Minister Martin Hamilton-Smith, former Labor MP Frances Bedford and Regional Development Minister Geoff Brock over their support for the Government’s policy on closed ICAC hearings.

However, he did not respond to a request for comment on whether the proposed judicial inquiry should hold public hearings.