One of the great achievements in water sustainability came in 2008, when eight U.S. governors came together to create the groundbreaking Great Lakes Compact, a pledge among their states and two Canadian provinces to protect the world’s largest supply of surface freshwater — lakes Superior, Michigan, Huron, Erie and Ontario.

Minnesota played a special role, with then-Gov. Tim Pawlenty becoming the first to sign the landmark agreement, which allows a single “no” vote to block any exceptions to the compact.

Now the compact faces its first real test, from a small, mostly well-to-do Milwaukee suburb in neighboring Wisconsin. Waukesha, pop. 70,000, says it needs to take up to 10 million gallons a day from Lake Michigan, because it has no “reasonable alternatives” to its own radium-contaminated groundwater. But Waukesha has failed to make a convincing case, and Gov. Mark Dayton should exercise his veto when the governors meet in June for a final decision on the city’s request.

Once Waukesha was renowned for its clean, refreshing springs, and even dubbed “Spring City.” But like many communities, it used its natural resources with abandon. Pollution spoiled many of the springs and others dried up. The city drilled deeper into its aquifers, and for the last two decades it has been pulling up water contaminated with radium, a health hazard. It is not alone.

A 2006 study showed that more than 40 communities in eastern Wisconsin had radium levels three times the federal limit. Existing water treatments, it should be noted, can remove up to 90 percent of radium. Tellingly, all of those communities but Waukesha have complied with federal standards or expect to do so, according to the Healing our Waters-Great Lakes coalition, which includes more than 100 groups that monitor the Great Lakes.

Waukesha chose to fight the feds in court for years, and now it’s under court order to comply with radium standards by June 2018. Time is running out, yet it continues to cling to an option most communities lack. The compact preserves Great Lakes water in part by limiting its use to those areas that fall within the natural boundaries of the Great Lakes Basin, stretching from northern Minnesota into Canada and east to New York state. Waukesha is wholly outside those boundaries, but Waukesha County straddles the line. The city is relying on that in its request to become the first exception to the compact. Environmental groups rightly worry about precedent, because an estimated 9 million people live in counties that straddle the basin. If Waukesha is made an exception, others are sure to follow.

To the city’s credit, it has undertaken a number of conservation measures — although not as early as some. The Wisconsin Department of Natural Resources, after more than five years of study, recently concluded that the city has no “reasonable alternatives,” that conservation would not do enough, that further water treatment would be too costly, and that drilling elsewhere could damage inland streams and wetlands. But other communities have had to undertake costly mitigation measures and strict conservation in order to produce safe drinking water.

Minnesota has its own water quality concerns. As rigorous as some think the state’s environmental standards, studies show that half of southern Minnesota’s lakes and streams are unsafe for fishing and swimming. Nearly two-thirds of test wells in the central part of the state have excessive nitrate levels. Restoring those waters will involve cost and hardship.

The water crisis in Flint, Mich., is only the beginning of an increased awareness of how fragile a resource clean water is. The compact is the primary safeguard for 20 percent of the world’s surface freshwater, and the pressure to tap that source will only grow in coming years. The Great Lakes governors should vote to protect that compact.