Treated effluent can be reused for the irrigation of parks and sports grounds but there is an associated potential public health risks from microbial pathogens present on the grass surface, particularly when used for contact sports. The main aim of this study was to investigate the survival of pathogenic and indicator microorganisms on the grass surface of a sports ground irrigated with treated effluent under differing climatic conditions. Results showed that Salmonella enterica serotype typhimurium, Escherichia coli, Enterococcus faecalis and Staphylococcus aureus decayed faster under direct sunlight than MS2 with one log(10) reduction (T(90)) varying from 3 to 11 hours. Rapid decay (T(90) 3 to 4 hours) of bacterial pathogens occurred in both sunlight and shade during the summer. In contrast, T(90) times for the bacteria during the winter varied from 6 to 11 hours in direct sunlight and from 23 to 38 hours in shade. No significant seasonal variation was observed in the inactivation of the bacteriophage MS2. Enteric viruses are expected to show inactivation rates similar to MS2. The results show that rapid inactivation of enteric bacteria can be expected on grass surface irrigated with treated effluent at higher ambient temperatures, in direct sunlight and low moisture content.