Pressure is mounting on a government agency to provide more answers over an $80 million taxpayer-funded water deal, with Labor demanding documents explaining the purchase be made public.

Key points: The company at the centre of the buybacks was once associated with Energy Minister Angus Taylor

The company at the centre of the buybacks was once associated with Energy Minister Angus Taylor In 2017, water licences were bought from two Queensland properties owned by that company, for $80m

In 2017, water licences were bought from two Queensland properties owned by that company, for $80m The Agriculture Department has stood by the deal but Labor wants related documents made public

In 2017, when Barnaby Joyce was the water minister, the Department of Agriculture and Water Resources bought 28 gigalitres of water from Eastern Australia Agriculture, a company once linked to now-Energy Minister Angus Taylor.

The deal was part of a series of controversial agreements which saw the Federal Government spend $200 million buying environmental water under the Murray-Darling Basin Plan. The buybacks occurred without an open tender process.

Opposition water spokesman Tony Burke on Monday wrote to the department asking it to publish, in full, documents relating to the due diligence and value of the deal.

Mr Burke is also seeking documents showing the department received advice from the Murray-Darling Basin Authority, State Government and Commonwealth Environmental Water Holder on the deal.

The letter follows a statement released by the department at the weekend defending the $80 million water buyback, and Mr Joyce yesterday laid the blame squarely on the Queensland Labor Government in a combative interview on Radio National.

"This is such a load of horse crap," Mr Joyce said.

"I'm 100 per cent certain that I have done nothing but my job and have nothing absolutely at all to hide."

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 48 seconds 1 m 48 s Tony Burke says questions remain over Murray-Darling buybacks

EAA is controlled by Eastern Australia Irrigation, which is based in the Cayman Islands.

Mr Taylor, a co-founder and director of Eastern Australia Irrigation, ended his association with the companies before entering Parliament in 2013.

Both he and Mr Joyce deny any involvement, but Mr Burke said the deal raised several questions.

"On the face of it, it looks like, for floodwater that only exists in very rare circumstances, that effectively, have paid very top dollar for it," Mr Burke said.

"You don't pay Versace prices for water that you get from The Reject Shop, and that looks like what Barnaby Joyce has done."

Prime Minister Scott Morrison has defended the deal.

"These arrangements were conducted at complete arm's length from any ministers," Mr Morrison said.

"The department has appeared before the Senate inquiry and has gone through the process that led them to that price and how it was transacted."

In its statement on Friday, the department said the purchase "represented a unique opportunity to secure a significant volume of water in a catchment of particular strategic importance to achieving the triple bottom line outcomes of the Murray Darling Basin Plan".

It also said claims the water could not be used off the property were false.

Mr Burke asked department secretary Daryl Quinlivan to respond by close of business on Tuesday.

The Greens have renewed calls for a royal commission into the Murray-Darling Basin Plan.

Frustrated Joyce points to Labor

Mr Joyce yesterday denied it was too much money to spend on water licences or that any government MP had profited from the arrangement.

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Asked to identify who profited from the deal, Mr Joyce evaded the question.

"It's not relevant. You don't ask that, you ask if they have water to sell. Not what clothes they wear, not who they are married to," he said.

Pressed further if he knew where the money went, Mr Joyce responded with frustration.

"Oh God. I've heard it's a trust account in the Cayman Islands — that's what the Queensland Labor Government should have told me. Shouldn't they? Water is a resource of a state government," he said.

"Why did Labor recommend it to us? Are they morons? Are they asleep? You're saying the Queensland Labor Government are completely incompetent and recommended us a bad deal?

"[It was a] Labor, Labor, Labor, Labor, Labor Government who recommended this to us."

Mr Joyce said he did not know the parties involved in the deal at the time.

"I never knew Angus Taylor. I wouldn't have known him if he stood up in my corn flakes before he came into parliament, right?" he said.

"There is nothing untoward about the actions of Mr Taylor — but he is the best person to interview [about that], not me, because I'm Mr Joyce.

"I am at arms-length. I do not negotiate the price. I do not negotiate the vender. I am responsible for the overarching policy. The Greens wanted more water, so we bought the water."