The study investigates the inactivation of biofilm bacteria colonized on the surface of polyvinyl chloride (PVC) pipes delivering either groundwater or treated wastewater. It does so using a citric acid (C6H8O7) solution. The results of the study showed that the optimal conditions of the biofilm bacteria inactivation were over 10,000 mg/L citric acid concentration and 60 minutes of contact time at least. Under these conditions, the removal efficiency could reach above 99.999% for heterotrophic plate count (HPC) bacteria and 99.95% for coliform bacteria. The study also showed that the biofilm bacteria were the major sources of planktonic bacteria resuspended into water purified by drinking water production systems (DWPS).