The carcinogenic potential of chlorine disinfection by-products and recent changes in water quality regulations have led to a greater emphasis on alternative disinfection mechanisms. In this study, the efficacy of bench-scale and pilot-scale titanium dioxide (TiO₂) photocatalytic disinfection was explored using four bacteriophages (MS2, PRD1, phi-X174, and fr). The optimized bench-scale experiments indicated that 1 mg/L of Degussa P25 TiO₂ irradiated by low-pressure ultraviolet (UV) light reduced the dose requirements for viral inactivation in comparison to UV light alone. The highest UV dose reductions for 4-log inactivation of PRD1, MS2, phi-X174, and fr were 19%, 15%, 6%, and 0%, respectively. Bench-scale photocatalysis was inhibited by limited adsorption of the viruses onto the TiO₂ nanoparticles, as indicated by the poor results for high TiO₂ concentrations. Subsequently, pilot-scale experiments were completed using the Photo-Cat Lab from Purifics. The annular reactor configuration and increased viral adsorption dramatically improved photocatalytic inactivation for samples with high TiO₂ concentrations. Using the Photo-Cat Lab, 2-log inactivation of the bacteriophages was achieved with 400 mg/L of Degussa P25 TiO₂ and a UV dose of approximately 34 mJ/cm² (energy consumption of 0.33 kWh/m³)—a 700-fold decrease in energy use compared to bench-scale photocatalysis.