That was the question on the lips of Boggabri cropper David Watt, as he watched Whitehaven spend hundreds of thousands of dollars outbidding farmers for groundwater.

“Whitehaven is already short of water at Maules Creek, but at the same time they are saying they don’t need any more licences to open up the new Vickery coal mine," Mr Watt said.

"It just doesn’t make any sense. It must mean their models don’t account for these kinds of dry times."

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However, the NSW Department of Planning (DPE) said the company was allowed to purchase more water to meet its planning consent, and if it couldn't secure enough the "consents require Whitehaven to modify operations on site to match its available water supply".

"The EIS for the Maules Creek mine predicted the water demand of the mine under different weather conditions, including extreme drought conditions, and the current impacts of the mines are consistent with these predictions," a spokesperson said.

"The existing planning consents for these mines do not impose restrictions on Whitehaven being able to import water from other sources."

Namoi Water executive Jon-Maree Baker said it was clear Whitehaven had relied too much on surface water.

"The Vickery extension will represent a significant increase in water consumption," Ms Baker said.

"The issue is not only have they had to go back to the market to source more water, but it calls in to question whether they've modelled correctly for a once-in-a-millennium drought."

A Whitehaven spokesperson said it would seek to accommodate all water requirements at Vickery from within its existing approved allocations, and the recent purchases did not change that position.

NSW DPE said the impacts of ground and surface water resources were key issues being considered in the Vickery assessment.