Developers and designers of municipal sewer rehabilitation programs are usually faced with the questions: • How effective will sewer rehabilitation be for reducing I/I and RDI/I (Inflow & Infiltration, and Rainfall Dependent I/I)? • How long can we anticipate that sewer rehabilitation will remain effective (how many years will we see benefits)? For this study, the authors collected seven years of publicly available treatment plant records extending over a period from 2001 through 2025. Treatment facilities in Tennessee are required to submit MORs (Monthly Operating Reports) to TDEC on a monthly basis. (Unlike the DMRs [Discharge Monitoring Reports] submitted to the US-EPA which only have monthly averages, these reports include daily influent flows, daily BOD/CBOD influent concentrations, and daily rainfall.) For each calendar year analyzed, 12 months of data were transcribed into a non-proprietary Excel spreadsheet. Using this process, annual I/I and RDI/I reports were generated for 2001, 2009, 2010, 2014, 2022, 2023, and 2025. From 1991 through 2003, the NOAP (Nashville Overflow Abatement Program) completed about 212 miles of sewer rehabilitation (or pipe replacement) projects. These rehabilitation projects also renewed over 5,000 service laterals. Twenty-six basin areas in the were monitored and analyzed which included 77 miles of sewer lining or replacement. A cumulative annual I/I reduction of 3.2 billion gallons was measured for these projects by before-after flow monitoring. The 26 projects represented about 1/3 of the rehabilitation work conducted through the program since 1991. The City of Nashville (and satellite areas) is served by three wastewater treatment facilities. The Central WWTP includes flows from areas served by combined sewers. It would be very difficult to measure I/I reduction from sewer rehabilitation in separate sewer areas at the influent to the Central WWTP since it is significantly influenced by direct inflow from the combined parts of its system. Therefore, for this study, we only evaluated the long-term I/I at the Dry Creek WWTP and the Whites Creek WWTP. The cumulative annual I/I for both plants in 2001-02 was about 12.681 billion gallons. In 2025, we observed that this figure declined slightly to 12.078 billion gallons (about 4.8% reduction). While RDI/I levels remained fairly stable the past 24 years at Dry Creek, RDI/I at Whites Creek appeared to increase. This increase may be connected to inflow defects in that system that may not have been addressed during lining operations. The cumulative reduction of annual I/I in these two systems since 2001 is much less than the reductions measured for individual project basins in the first decade of the OAP. This may be the result of the distribution of the various projects among the three WWTPs. It also may be a result of a change of overall strategy in the past 20 years to focus more on short term capture of excess flows in sewage detention basins.