Ms Hull handed out how-to-vote cards for her successor in the NSW seat of Riverina, Nationals leader Michael McCormack on Thursday.

At the weekend, Mr McCormack rejected calls for a royal commission from Howard government minister Amanda Vanstone.

But Ms Hull said the management, control and transparency of water trading needed a major inquiry.

"I would be advocating for us as the Nationals to lead that," she told AAP.

"There has been calls for a royal commission into water and as a past person who has represented irrigation I would absolutely support that."

Ms Hull, who now chairs Agrifutures, said a royal commission could examine whether water trading was open to fraud.

She believes the coalition is weighing the cost of a royal commission similar to the inquiries into banks, aged care and disability.

"I don't know that they're resisting. I think the case for the royal commission hasn't been articulately packaged together to give a clear understanding."

Ms Hull said voters were taking out "emotional frustration" on the Nationals in heartland seats, with the current drought in close proximity to the millennium drought.

"It's very difficult circumstances and time in the bush," Ms Hull said.

"The effects of the millennium are still being sourly felt in our electorates."

She backed Mr McCormack to continue as leader beyond the election, saying he was handling a tough job well.

"We are getting blamed for things that are really out of our control."

Australian Associated Press