The escalating challenge of water contamination by persistent organic pollutants needs the development of effective and long-lasting cleanup strategies. To improve photocatalytic and antibacterial performance, this study detailed the synthesis of pure and strontium-loaded zinc oxide (Sr-ZnO) nanoparticles using a simple co-precipitation approach. Structural, morphological, and optical characterizations employing XRD, FT-IR, Raman, PL, UV-DRS, FE-SEM, HR-TEM, EDS, and XPS demonstrated effective Sr2+ integration into the ZnO lattice without altering the wurtzite structure. Among the various loading doses, 3 wt% Sr-ZnO demonstrated the most efficient photocatalytic activity, attaining ≈ 100 % degradation of Reactive Red 120 (RR 120) dye under UV-A irradiation in 30 min and ≈ 100 % degradation under sunlight within 50 min. Improved charge carrier separation, longer light absorption, and enhanced reactive oxygen species (ROS) formation all contributed to improved performance. Optimal dye degradation occurred at neutral pH and a catalyst dose of 50 mg. Reusability testing revealed that after numerous cycles, efficiency exceeded 90 %. In addition to photocatalytic applications, 3 wt% Sr-ZnO was examined for antibacterial efficacy against Staphylococcus aureus, Pseudomonas aeruginosa, Bacillus subtilis, and Escherichia coli and showed significant bactericidal activity. Overall, the study establishes Sr-loaded ZnO, particularly at 3 wt% loading, as a highly efficient, stable, and environmentally acceptable nanomaterial for dye degradation and microbial disinfection. These findings highlight its enormous potential for integrated wastewater treatment systems, which provide a long-term solution for reducing chemical and biological contaminants in aquatic ecosystems.