The Linnwood Water Treatment Plant has 32 filters and the capacity to treat 275 million gallons of water per day. Water for the Linnwood Plant is drawn from an intake 6,565 feet from shore, five miles north of the Milwaukee harbor, at a point where Lake Michigan is 62 feet deep. The Linnwood Plant was completed in 1939.

As source water enters the first stage of water treatment, ozone is bubbled into the water from the lake in large contactor tanks. A highly reactive gas that destroys molecules with which it makes contact, ozone destroys illness-causing microorganisms and harmful compounds. It removes taste and odor compounds in the lake water, and reduces the formation of disinfection byproducts.

The next step is coagulation and flocculation. Aluminum sulfate (also known as alum) and polymer are added to the water to neutralize the charge on microscopic particles in the water. The water is then gently mixed to encourage the suspended particles to stick together to form floc.