Prime Minister Malcolm Turnbull moved the water portfolio back to agriculture under a deal with the Nationals following his elevation to the leadership last month.

But, negotiations are still underway to determine just who will have responsibility for what between Mr Joyce and his assistant minister, Liberal senator Anne Ruston.

Nationals senator John Williams told The Leader yesterday he was confident water responsibilities would end up with Mr Joyce and anything else would be unacceptable to his party.

“Anything other than that would be a misinterpretation of the agreement and that would not be good,” Senator Williams said.

He said moving water from the environmental portfolio to agriculture was one of the core concessions his party demanded from Mr Turnbull when he took over leadership of the Coalition.

“It was one of the key issues, if not the key issue, within the agreement,” Senator Williams said.

“It drove the party room discussions and my interpretation is water would be back with agriculture.

“I want to make it clear the water portfolio should, and I’m quiet confident it will be, controlled by minister Joyce, not by his assistant minister.”

Mr Williams said it made sense for water and agriculture to be under the same minister, as the two went hand in hand.

“Agriculture is where water belongs – what can be done in agriculture without water?” Mr Williams said.

A spokesperson for Mr Joyce said the New England MP was confident water would be under his control.