The central question in the 18-year-old, tri-state water war could be answered by the end of this year: Does metro Atlanta have the legal right to depend on Lake Lanier as its primary source of drinking water?

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In a four-page order issued Tuesday, U.S. District Court Judge Paul A. Magnuson said the answer may render other disagreements in the case "obsolete, or at the very least may invalidate" them.

He said a federal appellate court decision invalidating the region's short-term future claims to additional Lanier water "will undoubtedly affect this litigation."

Debate about the legal rights to Lanier's water has raged since Alabama filed the first federal lawsuit against the U.S. Army Corps of Engineers in 1990 to stop the Corps from giving metro Atlanta more water from Lanier.

Alabama and Florida say Congress established only three purposes for the 60-year-old federal reservoir: to control floods, float barges downstream and generate power. Supplying Atlanta's drinking water was an secondary benefit, they say.

Georgia strongly disagrees and has promised to prove in court that Congress intended drinking water supply as a main function of the lake. Lanier supplies water to more than 3 million metro Atlantans.

Gov. Sonny Perdue's spokesman Bert Brantley said "We're ready and willing to make those arguments and get this issue settled so we can get back to work on the real issue: how we share this resource."

Both sides said they are ready to negotiate out of court.

"The three states should reach an agreement, but only if there is a recognition that each state has to make compromises," Alabama Gov. Bob Riley said in a statement.