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In 1902, the Platte Cañon Filtration Plant, later renamed Kassler, was opened at the base of Waterton Canyon by the present-day Chatfield Reservoir. Kassler, which used the English slow-sand filter process, was the first of its kind west of the Mississippi River.

Kassler’s underground infiltration galleries were built in 1890, the filter beds completed in 1906, and the reservoir and pump station were built in 1972. A whole town was built around the plant to operate and maintain the facility. At the height of its operation, Kassler delivered more than 50 million gallons per day of treated drinking water to the residents of Denver. It was named a national water landmark in 1979.

By 1985, Kassler ceased operations because it was unable to keep up with demand. Now the buildings and nearby facilities are used for educational purposes.