AN AGREEMENT, under which water will be held in reserve in the Menindee Lakes, western NSW, for Adelaide's needs, has been described as "politically expedient". 

South Australian Liberal senator Mary Jo Fisher says the basis on which water is distributed must be clear, when there is not enough water.

That was the case with water in the Murray-Darling Basin, she said.

It was "imperative" there be a clear basis for water distribution in such circumstances.

But the necessary clarity and transparency had been lacking.

Adelaide's water had not come from the Menindee Lakes, Senator Fisher said.

But there had been a Council of Australian Governments agreement to reserve water there for Adelaide.

"Yet we have a politically expedient agreement," she said.

AAP