A senior government minister has rejected allegations a controversial $80 million water purchase verged on "corruption", amid calls for a major inquiry into the Murray-Darling Basin Plan.
Greens leader Richard Di Natale has led calls for a wide-ranging royal commission into the management of the river system after questions resurfaced about the government buying water from two properties in 2017.
"It verges on corruption and that's why we do need to see a full-throated investigation," he told ABC Radio National on Monday.
But Liberal campaign spokesman Simon Birmingham hit back at the Greens, describing Senator Di Natale's comments as scurrilous.
"We think a royal commission into allegations that are completely baseless would be a waste of time and money," Senator Birmingham told the ABC.
He said the company's original asking price had been more than $5000 a megalitre, but the agreed price was closer to $2700 a megalitre.
"The environmental and water department officials involved in the negotiation clearly drove a bargain to make sure they got an appropriate, competitive market price," Senator Birmingham said.
In August 2017, the government bought 28.7 gigalitres of water from two Eastern Australia Agriculture-owned properties, Clyde and Kia Ora, in Queensland at a cost of $78.9 million.
Eastern Australia Agriculture's parent company is based in the Cayman Islands, a well-known tax haven.
Labor has written to the Agriculture and Water Resources Department seeking by Tuesday copies of documents relating to due diligence checks, information about the validity of the licences on offer, proof that the sale met federal procurement rules, and advice provided by the state government, Murray Darling Basin Authority and Commonwealth Environmental Water Holder.
Labor frontbencher Tony Burke said some of this information had previously been released to the Senate in a heavily edited form, but it was now time to release it unedited.
The department has dismissed suggestions the water can't be used away from the properties, arguing the purchase has significant environmental benefits.
"This water was purchased for an environmental outcome. It was not, as is claimed, the largest purchase ever made," Senator Birmingham said.
Labor's Jenny McAllister said Barnaby Joyce, who was water minister at the time, needed to make it clear how the buyback represented value for money.
"$80 million on a water purchase, not through a tender process, what actually happened?" she told Seven's Sunrise.
Nationals deputy leader Bridget McKenzie said the previous release of documents was done following a "stock standard procedure".
Australian Associated Press