This study is aimed at the chemical synthesis of light-activated cobalt-doped zinc oxide and its further doping on reduced graphene oxide (RGO) and assessment of its antibacterial activity on antibiotic-resistant waterborne pathogens including Enterococcus faecalis, Staphylococcus aureus, Klebsiella pneumonia, and Pseudomonas aeruginosa. The synthesized nanoparticles were characterized via UV–vis spectroscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). The minimal inhibitory concentration (MIC) of nanoparticles portrayed a significant killing of both Gram-positive and Gram-negative bacteria. The synthesized nanoparticles were further found as active killers of bacteria in drinking water. Further, these nanoparticles were found photothermally active alongside ROS generators. The photokilling activity makes them ideal replacement candidates for traditional water filters.