But the sharpest attacks on the proposed regional compact are coming not from the distant Sun Belt but from within the Great Lakes states themselves as the plan is submitted to legislators for ratification.
Some communities in the eight states say the compact's strict limits on water diversion could leave them high and dry. Critics fear a torrent of lawsuits.
And supporters say the whole deal could unravel over an Ohio lawmaker's concerns about private property rights and insistence on rewriting provisions.
Backers are confident the plan adopted by the governors in 2005 will win needed approval by all eight states and Congress, but acknowledge it probably will take a few more years.
The longer the delay, they say, the greater the risk of losing control over the lakes - which, with their connecting channels and the St. Lawrence River, hold nearly 20 percent of the world's fresh surface water.
"It's OK to take a year or two to sort this out, but then they'd better buckle down and get on the same page," said Noah Hall, an environmental law professor at Wayne State University. "The real attacks are going to come in Congress, from states outside the region who don't want to see the Great Lakes locked up."
Skeptics doubt the supposed threat from the thirsty Sun Belt, saying shipping or piping water over such distances would have staggering costs and engineering challenges.
Still, "the time to put in place good water management is when you don't have a problem," said George Kuper, president of the Council of Great Lakes Industries, which represents companies such as Dow Chemical Co. and U.S. Steel Corp.
Despite the difficulties, grandiose diversion schemes have surfaced, including one entrepreneur's 1998 proposal to send tankers of Lake Superior water to Asia.
That idea quickly evaporated. But it inspired the governors to devise the Great Lakes-St. Lawrence River Basin Water Resources Compact, which treats the lakes and associated groundwater as one shared system.
It outlaws new or increased diversions, with limited exceptions, and also requires each state to adopt a conservation plan and regulate its own water use in keeping with common standards.
The Canadian provinces of Ontario and Quebec weren't included because U.S. states can't make treaties with foreign nations, but they signed a similar, nonbinding agreement.
In February, Minnesota became first to ratify the compact, which also has cleared the Illinois House and is pending in the state Senate. Bills have been introduced in Michigan and Indiana but aren't close to enactment. The matter is drawing little attention in Pennsylvania, where only the state's northwest corner is inside the Great Lakes drainage basin.
Among the issues facing lawmakers is the status of communities inside a Great Lakes state but outside the lakes' natural watershed.
Waukesha, Wis., a Milwaukee suburb, wants to draw water from Lake Michigan, only 15 miles away, but is just outside the lake's drainage area. The compact might allow the city to get its water because it's within a county that straddles the basin boundary, but that would require unanimous consent of the eight states' governors.
The Waukesha County Chamber of Commerce wants the deal amended so one state can't veto diversions to straddling counties. "Our argument is not to eliminate the compact. Our argument is to make sure it's fair," chamber spokesman Brian Nemoir said.
The pact appeared headed for approval in Ohio last year. But state Sen. Tim Grendell raised enough concerns to stall it. The Cleveland Republican particularly distrusts a declaration that Great Lakes water is held in public trust, saying that provision would void private ownership of farm ponds and even well water.
"The government is being encouraged to take people's property without paying for it. That is flat-out un-American," Grendell said.
Compact supporters say it honors existing rights. The public trust doctrine has been settled law since the late 1800s and balances needs of individuals and society, said Hall, the Wayne State professor.
The New York Senate balked last year at a provision allowing lawsuits against government agencies over failure to enforce the pact's standards. Backers say the compact grants no more access to the courts than other environmental laws, and allows states to handle local concerns under their own water-use rules. "The governors looked at all these issues and found ways to delicately handle them," said Molly Flanagan, a Great Lakes specialist with the National Wildlife Federation in Ann Arbor. "Now is not the time to renegotiate the deal. Now is the time to get it done." AP-CS-04-07-07 1320EDT