This study applied Cox proportional hazards regression to investigate the effects of environmental conditions—ultraviolet (UV) intensity, water temperature, and turbidity—on the time to complete inactivation of Escherichia coli (E. coli) during Solar Water Disinfection (SODIS). Regression data were obtained from 33 SODIS experiments carried out in Nsukka, Nigeria, over a five-month period from April to August 2021. The results revealed that both UV intensity and water temperature were statistically significant predictors of disinfection time. Specifically, an increase of 1 W/m² above the mean UV intensity (47.05 W/m²) increased the hazard of E. coli inactivation by 30% (HR = 1.30, p = 0.0002), while a 1°C rise above the mean temperature (44.85°C) raised the hazard by 122% (HR = 2.22, p < 0.00001). Turbidity, however, showed no significant effect (p = 0.97). The overall model was significant (likelihood ratio ?² = 93.73, df = 3, p < 0.0001), and the Nagelkerke pseudo R² was approximately 0.93, indicating a strong model fit. These findings suggest that UV intensity and water temperature are critical factors influencing the efficiency of SODIS, while turbidity within the studied range does not significantly alter bacterial survival outcomes.