The task force created by Gov. Sonny Perdue found that it would take at least eight years and hundreds of millions of dollars to bring new reservoirs online. And aggressive new conservation measures would not alone make up for the 280 million gallons a day the Atlanta area would lose if its supply from Lake Lanier dries up, the group concluded.
The findings place fresh pressure on Georgia to broker a deal with neighboring Florida and Alabama. The three states have been locked in a decades-long feud over water rights.
"Georgia absolutely must negotiate with the two other states," said Sally Bethea, director of the Upper Chattahoochee Riverkeeper.
In July, a federal judge found Georgia had few legal rights to drinking water from Lake Lanier, a federal reservoir in the north part of the state which serves as the main source of water some 3 million people in the Atlanta region.
U.S. District Court Judge Paul Magnuson gave the three states until 2012 to broker an agreement. If they fail to strike a deal, he said Atlanta's withdrawals from the lake would return to its level in the 1970s, when the city was a fraction of its current size.
Georgia is appealing Magnunson's ruling and has hired former U.S. Solicitor General Seth Waxman at a cost of $855 per hour to lead the high-stakes legal battle. Perdue has also rushed to jump-start stalled negotiations with Alabama Gov. Bob Riley and Florida Gov. Charlie Crist. The three are tentatively scheduled to meet sometime in December.
The task force was created to look at whether Georgia could go it alone if both the tri-state negotiations and the legal appeal fail.
One potentially explosive option contemplated by the task force would be to tap into the Tennessee River. That would almost certainly involve a politically charged lawsuit to move Georgia's northern boundary just a bit further north.
Georgia officials contend that a flawed 1818 survey mistakenly placed the state's northern line just short of the Tennessee River. That's kept water-starved Georgia from accessing a plentiful new source. But even if the state pursued such an option its estimated the water wouldn't be available until 2020.
Perdue spokesman Bert Brantley said it was simply one of many options on the table, but he allowed that Perdue's legal advisers are prepared should a lawsuit become necessary.
"We're not saying we're ready to pull that trigger," Brantley said. "But we certainly have done some additional legal work in that area."
The dispute traces back to a 19th century survey that misplaced the 35th parallel.
If Tennessee's southern border stretched along the parallel, as Congress decreed in 1796, Georgia would have a share of the mighty Tennessee - a river with about 15 times greater flow than the one Atlanta depends on for water.
The idea has been met with scorn by Tennessee lawmakers. Any border change would probably require an act of Congress or a U.S. Supreme Court ruling, so it's highly unlikely.