Metro Water Services (MWS) owns and operates the Omohundro Water Treatment Plant (OMO WTP) in Nashville, TN. With the earliest buildings constructed in the 1880s, OMO WTP is one of the few water treatment facilities on the United States National Register of Historic Places. In the middle of a major plant upgrade, MWS has been faced with the challenge of preserving historic facilities while modernizing treatment systems. One such system is the historic filters that are being converted to post-filter granular activated carbon (GAC) contactors. Built in the 1920s, the filters are a stunning example of craftsmanship and thoughtful design in public works of that era. With terrazzo floors and high arched ceilings, the filter building is the architectural centerpiece of the plant. As MWS modernizes and introduces new processes at OMO WTP, they resolutely protect this important piece of American water treatment history. The process advancements project began with an 18-month pilot study to explore emerging technologies to provide safe and reliable drinking water to Nashville. The pilot study results led to the selection of post-filter GAC contactors with an empty bed contact time (EBCT) of 10 minutes at plant capacity of 150 mgd. It was then decided through a rigorous alternative analysis that the existing filters would be converted to post-filter GAC contactors, and a new filter facility would be constructed. This plan provides new state-of-the-art filters, while maintaining the historic filters as an integral part of the treatment process. As the facilities around it undergo a once-in-a-generation overhaul, the existing filters will step into a second century of life as new sophisticated post-filter GAC contactors. From an aesthetic perspective, the building will appear unaltered. But behind the original brick façade, the process requirements will change dramatically, requiring significant renovations to the structure and careful coordination. This presentation will discuss the creative solutions that emerged from collaboration between MWS, engineers, architects, and the construction manager to preserve historic elements while executing substantial modifications. Through careful planning, coordination, and outside the box thinking, the new filters and post-filter GAC contractors preserve both the facility’s historic character and the robust process criteria and operability.