Urban wastewater contains a diverse array of human pathogenic viruses, often in high concentrations, presenting a significant challenge for water quality management. Sewage spills into natural water systems therefore pose a significant public health risk due to the potential to cause viral infections, yet the behaviour of viruses under dynamic environmental conditions remains poorly understood. This study investigates the decay of sewage-associated viruses (Adenovirus, Enterovirus, Hepatitis A Virus, Influenza A Virus, Norovirus GII, and Respiratory Syncytial Virus) in river, estuary, and marine water, with and without simulated sunlight. Using both qPCR and capsid integrity qPCR (CI-qPCR) methods, we found that in the absence of sunlight, time was the most significant factor influencing viral decay across all water types. The time required for a 90 % reduction in viral gene copies (T90) was observed within 0.3–24.3 days. Simulated sunlight accelerated viral decay, with significant reductions in gene copies l−1 observed within 1–3 days for all viruses studied, and T90 values ranging from 7 to 62.8 h. The effect of salinity on viral decay varied among viruses and water types. These results highlight the complex interplay between environmental water properties and viral persistence, emphasizing the critical role of solar radiation in viral inactivation. The study also demonstrates the value of using both qPCR and CI-qPCR methods to assess total and potentially infectious viral loads, respectively. These results have important implications for water quality management and public health risk assessment in diverse aquatic environments, particularly in the context of the increased frequency of sewage spills occurring in response to climate change and increasing urbanization. The data will support improvements in water quality modelling and associated risk management, contributing to more effective measures for protecting public health in coastal and inland water systems.