A final report on protecting water supplies in the northeast metro area confirms a price tag that could exceed $600 million. But it also cautions that lots of unknowns remain.

"This evaluation of alternatives stops short of identifying the best way forward," the Metropolitan Council said in a study released Monday, adding: "The best option for moving forward may be a hybrid of the examples considered in this study, and could involve approaches that were not considered in this study."

The study is just one in a sequence, from multiple sources, examining ways to deal with water problems in the area. The poster child is lake levels on White Bear Lake, which has lost a quarter of its contents in a decade.

Results aren't expected back on some key issues until 2016. But each advance in knowledge counts, said Barb Naramore, assistant commissioner of the Minnesota Department of Natural Resources (DNR).

"There are important ongoing studies, and additional insights to be gained" in how to manage water flows, she said. "We need to further refine and sharpen things."

A draft report in July had evaluated three basic approaches to address the problem, with costs ranging widely depending on factors such as the number of communities drawn into a solution.

Those solutions involved various ways of making use of water from the Mississippi River.

The final report also considers the option of relying on groundwater. But it hastens to note that "communities in the northeast metro could pursue less expensive approaches, which could include conservation or stormwater reuse to reduce groundwater pumping, before making large-scale investments in alternative infrastructure solutions.

"Such a plan could combine these less expensive options with aggressive monitoring of groundwater and surface water, and establish triggers for further action in the event these less expensive approaches are not effective."

As the science of water movement is pursued, a key political question as soon as the coming legislative session is the appetite of lawmakers to cover the cost of differing solutions, said Dan Pawlenty, public works superintendent in White Bear Lake.

"That's the wild card," he said, noting the flurry of studies in which it sometimes seems as though "everything is being thrown at us."

Among the initial price tags laid out in the final report, with each carrying smaller annual operating costs:

• $155 million if the St. Paul water system, drawing from the Mississippi, is expanded to serve Mahtomedi, Shoreview, Vadnais Heights, White Bear Lake, White Bear Township and North St. Paul.

• $169 million to $609 million if a new surface water treatment plant is built and water is moved from the river to the northeast metro. The difference in cost lies in things like capacity limits and number of communities included. Vadnais Lake would be a likely location for such a plant.

• $91 million if "existing community water supply systems … continue to be maintained," with new wells drilled as more water is needed. "Groundwater treatment facilities that are currently planned would be built." It's a cheaper option, and one that does maintain local control, but there's "potential for continued decline in aquifer and lake levels."

David Peterson • 651-925-5039