Notably, throughout the long process, the states and provinces had the Milwaukee suburb of Waukesha, Wisconsin, in mind as an eventual test case for their compact, which is now underway. A massive proposal by Waukesha to “borrow” up to 8.4 million gallons of Lake Michigan water every day (or 3 billion gallons every year) is weeks away from an up-or-down vote by the governors of the Great Lakes states.

Waukesha has had problems with its drinking water since the early 1990s, despite being situated in water-rich southeastern Wisconsin. Due to decades of unrestrained suburban growth, the deep sandstone aquifer that is its primary source of drinking water began to decline, resulting in concentrations of radium in the groundwater that exceeded Environmental Protection Agency standards established by the Clean Drinking Water Act of 1970. After an unsuccessful lawsuit contesting the validity of the EPA’s requirements, leaders of the roughly 70,000-resident city looked to the Great Lakes for a solution.

In eastern Wisconsin, a subcontinental divide marks the boundary of the Great Lakes drainage basin. Rivers and streams east of the divide flow into the Great Lakes. Waukesha, 17 miles west of Lake Michigan, sits just beyond its reach in the Mississippi River basin. The Great Lakes compact expressly prohibits diversions out of the basin. But there are exceptions. Communities that straddle the basin’s boundary line can win diversion rights with little more than state approval. The designers of the compact went further, creating a loophole that allows communities that exist totally outside of the basin—such as Waukesha—a chance at the lakes’ water. If these outlying cities or towns are in a county that straddles the basin boundary, they can apply for diversions as well.

The city of Waukesha, which lies in the straddling county of Waukesha County, formally submitted its application for a diversion in January—13 years after being prodded by a Wisconsin circuit-court order to have in place an alternative drinking-water source that meets EPA regulations for radium by June 2018. If approved, Waukesha would pump water from Lake Michigan to its water-treatment plant. In turn, as required by the compact, it would send the same amount back to the lake in the form of treated wastewater via a series of pipelines and via the winding Root River, which empties in downtown Racine, Wisconsin.

Proponents at a public hearing in February said the diversion is a no-brainer, a concept as uncomplicated as removing a teaspoonful of water from a swimming pool and returning it as clean as ever. The criteria, of course, are more elaborate. According to the compact, water returned to the basin must be equal in quality to the water taken out; diverted water will be allowed only if there is no “reasonable” alternate water supply available; a comprehensive water-conservation program must be in place; and the diversion must not affect the “integrity of the Basin ecosystem.”