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Ion exchange (IX) systems are widely used in drinking water treatment to remove charged constituents such as metals, nitrates, and other dissolved ions. While effective for chemical contaminant removal, IX resins may also provide a niche for microbial colonization, including opportunistic pathogens such as Legionella pneumophila. Despite the growing prevalence of residential and commercial IX systems, limited research has examined their potential to support biofilm formation or pathogen persistence. This study developed a bench-scale experimental method to assess the behavior of L. pneumophila in cationic (sulfonic acid functional group) and anionic (quaternary ammonium functional group) exchange resins over a 14-day period. Resins were conditioned for two weeks in the vessels to foster biofilm growth, after which they were inoculated with L. pneumophila and monitored under static batch conditions. Quantification of L. pneumophila was performed using IDEXX Legiolert and mip gene-targeted qPCR, while total bacterial biomass was assessed using 16S rRNA gene qPCR. The results showed consistent detection of L. pneumophila on resin surfaces over time, with higher persistence observed in the resin phase compared to the liquid phase. qPCR results demonstrated relatively stable gene copy concentrations throughout the study, contrasting with declining cultivability observed in Legiolert assays. This discrepancy suggests potential transitions to viable but non-culturable (VBNC) states or persistence of non-viable DNA associated with resin biofilms. Total bacterial concentrations remained high in all experiments, including in both cation and anion resins. While antimicrobial effects of QA resins could not be ruled out, further analyses are needed to evaluate resistance selection or inhibition.