WAUKESHA, Wis. — This city, once famous for its bubbling natural springs, sits about 17 miles from the shore of Lake Michigan. So when the state and federal authorities began demanding that the city address a growing contamination problem in its aquifer, the answer seemed simple: Get water from the big lake.

Surely, city leaders imagined, the needs of Waukesha, with a population just over 70,000, would be but a drop from the gigantic Great Lakes bucket, which amounts to one-fifth of the earth’s fresh surface water. That little drop, however, has stirred up a colossal struggle.

Waukesha has run smack into a landmark 2008 compact that prohibits large amounts of water from the five Great Lakes from being pumped, trucked, shipped or otherwise moved beyond the system’s natural basin without approval from the governors of each of the eight states that touch a lake — unless it is in a product like beer or soft drinks. Waukesha, despite being so close to Lake Michigan, is about a mile and a half outside the lake’s natural basin.

In a wetter era, the city’s plan to build a $200 million pipeline to tap into Lake Michigan might have fallen on more sympathetic ears. But it faces a daunting obstacle now: historic drought in the West, which has made officials in the Midwest more protective than ever of their increasingly valuable resource.