Source of Milwaukee water

FAQs - Water Quality and Public Health

The source of Milwaukee's water is Lake Michigan, one of the five lakes that comprise the Great Lakes. By size, it is the third largest of the Great Lakes and is the only one of the lakes that is contained entirely inside U.S. borders. Lake Michigan holds six quadrillion gallons of water. (source: Great Lakes Information Network)

Lake Michigan is the sixth largest lake in the world. The lake is approximately 307 miles long and averages 75 miles across, covering an area of 22,400 square miles. That is equal to the combined areas of the states of Maryland, Massachusetts, and Delaware. Lake Michigan has 1,638 miles of shoreline including islands.

Lake Michigan is 335 feet above Lake Ontario and 577 feet above sea level. The lake averages 279 feet in depth and reaches 925 feet at its deepest point.

The lake's drainage basin is 45,600 square miles and includes portions of Wisconsin, Illinois, Indiana, and Michigan. In Wisconsin, 30.7% of the land mass is within the Great Lakes Basin.

Lake Michigan's cul-de-sac formation means that water entering the lake circulates slowly and remains for a long time (retention) before it leaves the basin through the Straits of Mackinac. Scientists have calculated that the water in the lake replenishes over a period of 99 years.