This would occur if deep cuts to the territory's water allocations go ahead.
Under the guide to the Murray-Darling Basin Plan, released last Friday, the ACT would lose at least 13 gigalitres of water, or 34 per cent of its supply, and 18 gigalitres, or 45 per cent, at the top end of the spectrum.
ACT Water Minister Simon Corbell said yesterday the Murray-Darling Basin Authority seemed to have lost sight of the fact that the capital was reliant upon the basin for its urban water supply.
"Canberra is the only urban settlement in the basin entirely dependent on water from the basin for our water supply," Mr Corbell said.
Mr Corbell said the ACT government had reached an agreement with the Rudd government in 2008 that stipulated the future growth of the city would be taken into account when any cap on water allocation was implemented.
He said the ACT was prepared to make a "reasonable contribution" to returning water to environmental flows, but Mr Corbell said if the territory needed additional water it would have to purchase it on the market.
"If this was to occur we would ask the commonwealth to provide us with assistance for this. It is unfair to expect the territory to shoulder that burden entirely itself," Mr Corbell said.
A spokesman for ACTEW, the government-owned company that provides water to Canberra residents, said if the allocations flagged by the MDBA were to be rolled out across the basin, "we would have to constrict water use or find sources of water from elsewhere".
The comments came as Environment Victoria said the 27 per cent to 37 per cent reduction in water allocations flagged for the irrigators in the basin were not deep enough.
The NGO's chief executive, Kelly O'Shanassy, said rivers might require up to 7600 billion litres of extra water to return to health, rather than the 3000 to 4000 gigalitres the authority recommends be be returned to the environment.
Tony Abbott said under the current recommendations of the authority, towns such as Griffith in the NSW Murrumbidgee region would be devastated.
"All of us are in favour of trying to improve the environmental health of the Murray-Darling Basin, but you cannot do it in ways which destroy our agricultural industry and compromise the future of these regional communities," the Opposition Leader told Sydney's 2GB radio.
"The last thing we can do is penalise decent, honest farmers for the mistakes that governments have made."
Mr Abbott said it was "perverse and crazy" that a country such as Australia had become a net importer of food.