<p>Early research has found that biofilms adhered to treatment filtration beds and the inside of drinking water pipes help promote antimicrobial resistance (AMR) in drinking water systems. This study investigates the impact of a sub-minimum inhibitory concentration of ciprofloxacin (10 µg L^–1) on AMR and antibiotic resistance genes (ARGs) in multi-species biofilms formed on polyvinyl chloride pipe using a novel bench-scale water distribution reactor. The biofilm was grown from drinking water and contained a highly diverse composition consisting of, but not limited to, <i>Dechloromonas</i>, <i>Pseudomonas</i>, <i>Pseudoxanthomonas</i>, <i>Acidovorax</i>, and <i>Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium</i>. It was found that when the biofilm was exposed to ciprofloxacin, the total cell counts significantly increased, suggesting a potential AMR response. <i>IntI1</i> and <i>sul1</i> showed a significant inverse correlation with several genera as well as with increased diversity. <i>Asinibacterium</i>, found at a lower abundance in the biofilms, had a significant positive correlation with <i>intI1</i>, indicating its potential role in ARG promotion and the enhanced risk of a less diverse biofilm. This study highlights the need for targeted control strategies against AMR development in the context of drinking water distribution systems, emphasizing the role of biofilm community composition and residual antibiotic exposure.</p>