TAMWORTH MP Kevin Anderson has flatly refused to consider doubling the capacity of the new Dungowan Dam for an additional tenth of the cost.
The $480-million dam will be the most expensive dam per megalitre ($21.3 million) 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.
However, Mr Anderson rejected the idea.
"We've got this far, the time for talk is over. We fought so hard to get it, now it's time to get on to it.
"Other people can consider it if they want, I am focused on getting the dam started."
The dam is not expected to be completed until 2024 at the earliest.
University of NSW water expert, Professor Stuart Khan, said it was better to ask these questions before construction started.
"It's a good question to ask," Professor Khan said.
"We don't want to be in a situation where we might want to expand it again, and look back and ask why didn't we spend the extra 10 per cent."
Professor Khan said when it came to dams, it wasn't just the size that mattered. "The yield is actually more important," he said.
"It's the amount of water that falls in the catchment. There is a maximum optimal size for every dam, and it may not have a sustainable yield at that size.
"The key question is not how much bigger the new Dungowan Dam could be, but how much extra yield we could get out of it.
"If we could get another 40 per cent yield for an extra 10 per cent, I think for sure we should be looking at that."