CHICAGO — Representatives of the eight states in the Great Lakes region are preparing to decide whether a city in the Milwaukee suburbs qualifies to tap Lake Michigan as its drinking water source.

Waukesha, Wisconsin, said the groundwater wells on which it has long relied are contaminated with radium. The city is only 15 miles from the lake. But because it lies just outside the Great Lakes watershed, it needs permission from all the region’s states to use lake water.

They include Illinois, Indiana, Michigan, Minnesota, New York, Ohio, Pennsylvania and Wisconsin.

Waukesha said it would return as much water as it uses. Opponents said the city has other alternatives and approving its request would set a precedent that could lead to demands from other communities near the watershed boundary.