Double Dungowan Dam size for an extra one tenth of the cost

There are still many unanswered questions regarding the $480-million dam, including its size. Currently, it's pegged to be 22.5 gigalitres and will be among the most expensive dams per megalitre ($21.3 million) ever built in Australia.

A report by Water NSW shows that for an additional $46 million, the dam could be doubled in size to 40GL, dropping the price per megalitre to $13.15 million.

For an additional $89 million, the dam could be expanded to 60GL, dropping the per megalitre price to under $9.5 million.

The final size of the dam is likely to be influence by a number of factors, including if additional land must be purchased, how much extra water the region can draw out of its allocation from the Murray Darling Basin Authority and if a larger dam would still have an effective yield.

Shooters, Fishers and Farmers spokesperson for Tamworth, Jeff Bacon, said it's something the government should consider given the magnitude of the decision.

"This is a once-in-a-generation opportunity to build a dam and we have an obligation to do it right the first time round," Mr Bacon said.

"If there is a little extra expenditure to potentially double its capacity, commonsense says you would do that."

NSW Business Chamber regional manager Joe Townsend said it was hard to comment one way or the other without seeing a business case, however implored the government to consider all options.

"We always rely on water security, and the greater water security is, the greater the investment from private sector," Mr Townsend said.

"No matter what the decision, we just need to see the dirt start to turn so business confidence can return."