Lack of improved drinking water sources contributes a lot to many waterborne diseases caused by pathogens which include viruses, protozoa, bacteria or worms. It is essential to develop and promote treatment methods in order to provide pathogen-free safe drinking water. Sunlight plays an important role in disinfection of viruses through direct photolysis or indirect photolysis through reactive transient species such carbonate radical. This study demonstrated that carbonate radical can be generated using 4-carboxylbenzophenone (CBBP) as sensitizer to react with carbonate/bicarbonate ions. The steady state concentration of carbonate radical was determined by measuring the degradation of probe compounds using HPLC. 4-nitroaniline proved to be an appropriate probe compound to be used in this method. CBBP concentration was varied in order to generate different carbonate radical concentrations and subsequently vary the inactivation rate. The measured carbonate radical concentration varied from 10-14 to 10-12 M which corresponded to the values obtained from previous studies. The resultant inactivation kinetics showed that the reaction order of carbonate radical was 0.13±0.064 which may be due to the surface reaction or the interference of 4-NA. The pseudo-first order inactivation rate constant of Phi-X174 bacteriophage was 5 times smaller than that of MS2 while bacteriophage GA had similar inactivation rate constant with MS2.