In an argument before the U.S. Supreme Court Monday, a lawyer representing Florida seemed to gain ground in the state's effort to gain water that it claims Georgia has unfairly siphoned off to serve thirsty Atlanta-area residents.

“Florida has suffered real harm” from Georgia's “unreasonable and in fact unrestrained” over-use of water from the Apalachicola River, Latham & Watkins partner Gregory Garre told the justices in the case of Florida v. Georgia.

The dispute was before the high court under its “original jurisdiction” to referee disputes between states without first being heard by lower courts.

Garre said that Ralph Lancaster Jr. of Pierce Atwood in Portland, Maine, the special master appointed by the Supreme Court to build a factual record and make recommendations in the case, had made “a legal error” by urging the court to dismiss Florida's complaint.

While acknowledging some harm to Florida from Georgia's actions, Lancaster said there was no “clear and convincing evidence” that a ruling in Florida's favor could produce a remedy that would fix the problem. Without this “redressability,” Lancaster said, the complaint should be denied.

But several justices on Monday appeared to embrace a simple rationale that favored Florida—basically, that any reduction in Georgia's use of water from the river would mean more water for Florida's fisheries and oyster industry.

“You have common sense on your side,” Justice Elena Kagan told Garre, though she later also said there was “kind of a vacuum” in precise predictions of how much water would end up in Florida if a cap on Georgia's consumption was ordered.

Garre responded that, during fact-finding and a six-week trial before Lancaster, Florida had provided “significant evidence” that Florida would benefit and that in court precedents in previous water disputes, “absolute precision is not required.” He added, “We meet redressability under any standard.”

That seemed to satisfy some justices, putting Kirkland & Ellis partner Craig Primis, who represented Georgia, on the defensive, insisting that Florida had not proven its case.

But Chief Justice John Roberts Jr. told Primis, “It seems to be asking a lot of Florida” to require precise estimates of the benefit to Florida if Georgia was reined in.

Primis took another tack, countering the seemingly simple notion that less water for Georgia means more for Florida. “It's incredibly complicated,” he said. Other stakeholders are involved, he added, as well as considerations such as water quality, navigation and the need to prepare for droughts.

Justice Stephen Breyer offered a hypothetical, asking whether Florida would benefit if the mayor of Atlanta decreed that residents drink less water and more Coca-Cola—though at first he mentioned Pepsi, a nonstarter in the city where Coke is headquartered.

“Yes, it would be Coca-Cola,” Primis said amidst laughter. But his answer was the same—that “it's not that simple.”

One reason Lancaster had expressed doubt about whether Florida's complaint could be remedied was that the U.S. Army Corps of Engineers, which manages five dams and the water flow in the river basin, was not a party to the case and therefore could not be ordered to solve the problem. The United States had refused to waive sovereign immunity in the case.

“Why is the United States not in this case?” Breyer said at one point, adding that he had seen only “mystical answers” to the question.

Deputy U.S. Solicitor General Edwin Kneedler told the court that, unlike in some other water systems, Congress had already laid out Army Corps priorities for the river basin at issue, so that the court should not order the corps to take action. “This is a difficult case.”

But several justices seemed ready to issue a decree in Florida's favor anyway, in the belief that the Corps of Engineers would be likely to heed what the Supreme Court had to say.

In rebuttal, Garre seemed to agree. “There is no reason to assume that the Corps would ignore a decree.”