The diversion sidesteps a key piece of water policy that is commonly called the Great Lakes Compact. The compact, along with Ontario and Quebec’s parallel agreement, is a protocol for when water can be taken outside the basin — which is to say, almost never. But there are exceptions for cities and counties that straddle the watershed boundary. With its groundwater contaminated by naturally occurring radium, Waukesha, Wisconsin, went through an intensely scrutinized application to take water from Lake Michigan. It took seven years, including legal appeal, before the diversion was finalized.