James W. Jardine Water Purification Plant
Opened in 1964, this plant treats 1.4 billion gallons of water per day. It's on a man-made peninsula jutting out into Lake Michigan. It supplies water to around 64% of the city's residents. Read more about it here: https://www.enr.com/articles/43361-the-10-largest-drinking-water-treatment-plants-in-the-world