A letter by 12 independents, released to the media on Monday, calls for a "tough National Integrity Commission" to take immediate action and investigate water buy backs.

Pressure is mounting on the federal government to provide more answers over an $80 million taxpayer-funded water deal.

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.

Independent candidate for Cowper Rob Oakeshott and Independent candidate for Lyne Jeremy Miller signed the letter.

Mr Miller said he signed the letter because he believed in "honest politics".

"There is an old saying that sunlight is the best disinfectant," Mr Miller said.

"We need to bring any allegations of shady dealings into the sunlight so we can restore trust.

"That means a Federal Integrity Commission with real teeth that can look into these issues."

Mr Miller said the public need answers before the federal election.

"People need to know the real story before they cast their votes."

Mr Oakeshott said he signed the letter because he was concerned about a misuse of public funds.

"I am concerned that questionable water buyback policies are taking money that could be coming to much needed projects improving coastal wetlands and our local river systems," Mr Oakeshott said.

"For a local member, there are river health and small business issues at stake in this - and there are obligations to the national agenda."

Prime Minister Scott Morrison hosed down calls for a royal commission into the Murray-Darling Basin plan on Monday, defending Angus Taylor and Barnaby Joyce, who held the water minister at the time.

"These arrangements were conducted at complete arm's length from any ministers," Mr Morrison told reporters in Melbourne.