A virtually unused desalination plant in South Australia will be fired up over summer as part of an effort to help farmers in drought.
The Commonwealth has struck a $98.4 million deal with the state government so the plant can be used to service Adelaide.
This will leave 100 gigalitres of Murray River water to grow fodder upstream.
Up to 6000 irrigators will get access to 25 megalitres, which must be used to grow feed for their livestock.
South Australian Water Minister David Speirs said farmers across the country were crying out for help.
"Given our desalination plant sits virtually unused, it's time to increase its production so water is made available to drought-affected farmers across the nation," he said.
South Australia has agreed to supply an initial 40 gigalitres by the end of April.
The deal will then be reviewed, with the remaining water likely to be released.
Nationals Farmers Federation president Fiona Simson said shoring up fodder supplies was important, but she had questions about how the scheme would work.
"We are keen to understand more of the detail around exactly how the 100 gigalitres of new water will be allocated and managed for southern basin fodder producers," she said.
Labor water spokeswoman Terri Butler said it was time to release the feasibility study into the desalination plant, which was due to presented to government in March.
"We need it so we can get a sense of whether the decision to turn on the plant is aligned with the science and what other opportunities are there to use the desalination plant," she told AAP.
"We also want to know how the one-off water arrangement will work."
She said it had only been necessary because the government had done nothing about drought resilience.
South Australian Greens senator Sarah Hanson-Young is deeply sceptical.
"The Murray Darling Basin has been riddled with dodgy accounting, mismanagement and outright water theft," she said.
"Why should we believe putting the National Party in charge of spending another $98.4 million worth of water will be managed properly and above board?"
South Australia has also been given $10 million for its own drought mitigation and support measures.
Australian Associated Press