The government rejected several offers from Eastern Australia Agriculture over the past decade to sell its overland-flow water rights because the deals were “not value for money”, before paying $80m for the same rights, new documents show.

The water purchase in the Condamine Balonne catchment has been controversial because it cost taxpayers $80m, was concluded without tender and the company was founded by the energy minister, Angus Taylor.

But Taylor says he had ended his association with EAA before entering parliament in 2013 and was unaware of the $80m sale before it was announced.

The water deal was also controversial because overland flows are irregular. Since the deal was done in 2017, the commonwealth has received not one drop of water due to the drought.

Now the new documents, which were produced late last year in response to Senate estimates’ questions on notice, raise more questions. They show that EAA offered to sell its water entitlements, including the overland flows, on three earlier occasions but its offers were judged to not be value for money.

An analysis of the information by the Australia Institute says the new documents raise additional questions about the $80m purchase price.

In 2008/09 EAA offered to sell more than 37,000ML of overland flow for $1,495 a megalitre. But this was rejected by the Commonwealth as not value for money. In 2013-14 and again in 2014/5, the company again offered to sell a portion of its overland flows but its offers were rejected for the same reason.

Yet in 2017 the then agriculture minister, Barnaby Joyce, agreed to pay $2,745 a megalitre for the same water entitlements.

“That is higher than any previous offer by EAA and almost double [84% higher] the previous offers that the department considered too expensive,” the Australia Institute’s senior water researcher, Maryanne Slattery, said. “There has been very little variability in water prices in the Condamine-Balonne since 2008/09 and the price increase cannot be explained by increased market prices.”

The government has refused to release independent valuations of the water rights, despite requests from the Senate, and instead released documents that are so heavily redacted as to be meaningless.

Four water purchases – all conducted without tender in 2017 – including the $80m EAA deal and another $80m water purchase from Tandou are now under scrutiny from the auditor general. The report is expected by March.

The new documents also mention Growth Farms Australia, a company in which Taylor has an indirect shareholding, through his family investment company. It is declared in his pecuniary interests register.

The new documents say the consultant for EAA, Tony Reid, was attending a negotiation with the department “as a director of Growth Farms” in the negotiations for the water sale.

Reid, who remains a director of Growth Farms, has several business interests with Angus Taylor and his family. He told the Guardian it was an error by the department to say he attended as a Growth Farms director.

Previously he has told the Guardian that he was acting as an individual when he consulted to EAA on the sale of its water to the government in 2017.

“I personally and independently, through my own personal company, worked for EAA from April 2010,” he said. “I can take no responsibility for various media or government entities getting their facts wrong.”

Growth Farms was responsible for the management of the two huge cotton properties in Queensland until 2010, when the contract ended, but Reid continued his association.

Taylor, who was a director of EAA in 2008/09, has said he ended all association with the company when he became a parliamentarian.