Wednesday's disallowance prompted the Berejiklian government to declare the entire basin plan "untenable". By Thursday, though, NSW Minister for Regional Water Niall Blair was wavering in his promise to pull NSW out of the plan, voicing hope the Turnbull government could work with Burke "to come to a position". Victorian Premier Daniel Andrews had also softened Minister for Water Lisa Neville's comments that her state would "walk away" from the plan, saying his government would co-operate with Canberra "to find a way forward". Some cooling off was always likely a week after Littleproud dubbed Labor senators "traitors and turncoats", guilty of "an act of bastardry" if they supported the motion. But how did disagreement over a proposed cut of 70 billion litres - or about 2.5 per cent of the proposed 2750 billion litres in annual environmental savings - and perhaps 200 jobs escalate into such a stand-off?

Loading Replay Replay video Play video Play video For veterans such as John Williams, ex-head of CSIRO's land and water division and a founder of the Wentworth Group of Concerned Scientists, such efforts to tinker with the plan are nothing new. Rather than hanker for some backroom compromise - presumably after the SA elections on March 17 - Williams hopes the brinkmanship triggers a truly independent examination. Too little is known about much of the water savings actually make it to the environment or get captured by some big user - typically an irrigator - in some valley downstream. About 75 per cent of the northern basin water extraction is unmetered, compared with an average of about one-third unmonitored on average across NSW. "It's basically an honesty box system," one insider says.

"The fox has been in charge of the hen house," Williams says, questioning the authority's autonomy. "Let's have an independent audit to see if we've been getting the benefits we've spent billions on." The case for reforming the Murray-Darling was driven in the 1990s by rising salinity, large areas of dying river red gums and a general decline in the native fish and aquatic vegetation, Williams noted in a paper last year. An 1995 audit for the ministerial council demonstrated river systems "seriously stressed, largely due to the excessive extraction of water for irrigation", his paper states. The council report stated drought that would have occurred in "one in 20 years under natural conditions, is now happening in six out of 10 years". While the long-term median flow in the basin is about 14,000 billion litres a year, dams and other storages had expanded with little check to total 35,000 billion litres, Williams wrote. Preliminary estimates by scientists in 2002 indicated annual extraction levels should shrink about a third, or 4000 billion litres, with the water saved returned to the rivers, wetlands and other natural systems to restore their health.

By 2010, the basin authority itself put the minimum savings requirement at 3860 billion litres a year. After public protests, particularly in irrigation communities such as the Riverina, the plan had scaled back the necessary annual savings to 2750 billion litres by the time the scheme was enacted in November 2012. "I do not understand the science, economics, social science or engineering use to arrive at this figure of 2750 (billion) litres a year," Williams wrote. "I have never seen the quantitative evaluation of this calculation." Later negotiations lifted the environmental water tally by 450 billion litres to 3200 billion litres provided additional funds could be found - a promise Labor's Burke this week was seeking in exchange for not blocking the 70 billion-litre amendment. The lack of transparency underpinning calculations was also a major reason why Mal Peters, formerly chair of Northern Basin Advisory Committee (NBAC), rejected the proposed 70-billion litre cut.

Peters laid out a slew of concerns in a scathing submission to the Northern Basin Review. "Throughout the process, NBAC was seldom confident that the MBDA were giving them the information necessary to fulfil their charter and we believed [the authority] at times withheld or provided misleading information," the submission states. In an unusual move, the authority submitted a retort to Peters - an action it didn't take for the other three NBAC members who posted critical individual reports. Peters' submission was "surprising and disappointing", and the authority "wholly rejected" what it called "unfounded assertions about the research and science" underpinning the review. But Peters, an irrigator and long-standing advocate for rural communities with roles including heading the peak agriculture lobby NSW Farmers, is adamant the review was flawed.

"There was no confidence in hydrological and socio-economic numbers, the peer-review, all these issues with the Barwon-Darling, the flows into South Australia, (and) no confidence in the process," Peters tells Fairfax Media. "It became quite clear that the modelling was very questionable, and we pushed them to get it peer-reviewed," says Peters. "Then we found out subsequently that he's a paid consultant [who] does a heap of work for the authority." Two former senior authority staffers share Peters' doubts. Maryanne Slattery is now the senior water researcher at The Australia Institute, but was previously at the authority for more than a decade, including five years as its director of environmental water policy. Maryanne Slattery, a former Murray-Darling Basin Authority staffer, says satellite imagery pointing to possible water theft was ignored. Credit:Dion Georgopoulos

Among many issues Slattery raises are the "rubbery figures" - as the institute described them in a recent report - that reveal how the authority made multiple changes to its estimated impacts of the northern basin amendments. According to the initial versions of the "final report" in November 2016, South Australia stood to lose 20 billion litres and Menindee Lakes - the main water supply for Broken Hill - 35 billion litres per year. "Such a large impact would almost certainly have been rejected by South Australia," Slattery wrote. A year later, the reduced flows had shrunk to 4 and 7 billion litres, respectively.

"[T]here has been no disclosure of why most of these changes were made, or presentation of analysis or modelling to support them," Slattery wrote. The authority, though, said it stood by its "rigorous and independent assessment of downstream impacts". Slattery tells Fairfax Media the authority was also well aware of NSW compliance issues related to alleged water theft in the Barwon-Darling - one of the regions that stood to have got some of the 70 billion-litre savings - well before ABC's Four Corners aired the claims last year. "NSW has been threatening to pull out [of the plan] since 2014," she says. The authority's fear "of not wanting to upset the states was a large part" of why it didn't use its own powers under the Water Act to curb rorting. Bill Johnson, a former NSW environmental water manager who later became director of Northern Basin Engagement for the authority, says the authority knows precisely where to probe for non-compliance.

"They don't need to look at the whole basin," Johnson says. "They know exactly where the water is coming out." According to Slattery, advances in satellite imagery such as the Data Cube developed by Australian Geoscience offered the authority technology that could track environmental flows. Loading They turned the remote-sensing on to watch the release of about 9 billion litres of water bought by the Commonwealth Environmental Water Holder into the Gwydir River. "Almost immediately, it became clear it was being extracted as soon as it got into the Barwon-Darling," Slattery says. "We had multiple lines of evidence that suggested the water was being taken."

To her surprise, however, the final report covered a shorter period and a more narrow geography, excluding the main finding. Also, "they picked satellite images that were really poor", she says. "We found that the technology was promising but more was required to turn the information into evidence of any illegal actions," the authority tells Fairfax Media. "We formally referred concerns about alleged illegal water take in the Barwon Darling to WaterNSW and NSW [Department of Primary Industries]." Mark McKenzie, chief executive of the NSW Irrigators Council, says "due process needs to be followed" in the various inquiries still under way, including an investigation by NSW's Independent Commission against Corruption. "There's an enormous assumption [allegations raised by Four Corners and elsewhere] were all true," he says.

"We have zero-tolerance for theft of water," McKenzie says, adding that anyone found to have done so, "should have the book thrown at them". Downstream costs are mounting for taxpayers in other ways. Thursday saw what organisers say was the first public protest against the start of construction of a $500 million pipeline to suck water out of the Murray at Wentworth and pump it 270 kilometres to Broken Hill. Jane MacAllister, a Wentworth councillor, says "there is so much we don't know about" the pipeline, including its business case and how farmers on the lower Darling will fare. "We need a national water ombudsman and a federal water registry, with real-time monitoring of water use," she says.

While NSW's water minister Blair is understood to see political gains in western NSW for Nationals in pulling out of the plan, urban taxpayers may be less forgiving particularly if they see more evidence of wastage and little to show for the spending in terms of environmental results. At the end of the southernsystem, flows at the Murray mouth sufficient are insufficient to clear the barrages, harming the Coorong, says Fiona Paton, an environmental engineer with the University of Adelaide. "The seedbank of Ruppia tuberosa, a key aquatic plant of the Coorong [a Ramsar wetland], remains impaired and so lacks resilience to respond to future droughts," she says. "Numbers of migratory shorebirds, for which we have international agreements, are also dwindling and these birds are struggling to find enough food." Challenges to come include "accounting for the impacts of climate change, which the plan does not consider", Paton says. Another big challenge could be the plan's failure to account for the loss of so-called return flows, where other nations such as the US do.

Water that used to seep back in to the river system from irrigation channels, say, is now being captured. With the buybacks of water capped by the Abbott-Turnbull government at 1500 billion litres, the bulk of the plan's money is going on the more expensive infrastructure work to improve on-farm efficiency of water use that would typically reduce those return flows. Williams, who expects to publish his findings in Science journal soon, says the basin's environment could be missing out on 100s of billions of litre a year, underscoring the need for a thorough audit. "This is critically important," Williams says. "Unless you know the return flows, you don't know how much you've saved."