The debate is taking center stage as Georgia fights for a greater share of the region's water supply.
State officials said there's about 80 days' worth of drinking water left in Lake Lanier, which supplies 3 million people with water.
But the Army Corps of Engineers, which manages the region's water sources, contends there's enough left for about 280 days, with more than half of it stored in the so-called "dead pool" _ inactive storage at the bottom of the lake.
The pool is below the level of most water system intake pipes, and accessing it would be time consuming and expensive, state environmental officials said.
"Is there water there that could be used? Yes," said Carol Couch, director of the state's Environmental Protection Division. "But it's not exactly high quality."
Gov. Sonny Perdue, who has long argued the water at the bottom of the lake is "suspect," is headed to Washington on Thursday to lobby for water rights in a tug-of-war with Florida and Alabama.
The governors of the three states are slated for a three-hour meeting with Interior Secretary Dirk Kempthorne and other Bush administration officials in an effort to reach a temporary agreement.
Perdue has blamed the Corps for releasing too much water to protect endangered mussels in Florida.
The Corps has determined that many industrial and municipal users in Alabama and Florida could tolerate reduced flows in rivers, but it remains unclear how much of a reduction would be acceptable, a top official said Wednesday.
"What it comes down to is whether we can reduce the flows enough to still save the species and meet all the users' needs downstream," said Maj. Daren Payne, deputy commander of the corps' Mobile, Ala., district. "We're finding now that the power plants and a lot of the other interests can operate at something less than the current flows."
The Corps will release a biological assessment for species impacts by Friday, laying out several options for altering the water releases from the federal reservoirs, Payne said.
Instead of pointing fingers over endangered mussels downstream, officials should be looking at ways the Atlanta region can better handle growth and encourage conservation, said members of the Georgia Water Coalition, a consortium of environmental groups. "The water crisis in metro Atlanta is largely due to mismanagement of existing resources," Upper Chattahoochee Riverkeeper Sally Bethea said at a news conference outside the state Capitol.
Instead of building additional reservoirs in North Georgia, as legislative leaders have suggested, the state should be spurred by the current drought to look at ways to use what it has more efficiently, Bethea said.
The group said the region relies too much on septic tanks, which are slower than sewer systems in returning waters to rivers.
The Corps, which is in the middle of the water fight, still maintains there's plenty of drinkable water left.
"No one's endangered of running out of water any time in the next six to eight months," said Major Daren Payne, the deputy commander of the Corps' Mobile office. "We could go for a long, long time. And if we get any rain, it extends the amount of time we could go."