Pristine ZnO nano-sized particles, naked and/or sensitized can be used as effective catalysts for water disinfection by degradation and complete mineralization of two gram negative bacteria with direct solar light. Unlike earlier studies, which showed that ZnO particles caused death and growth inhibition only, the new results show for the first time that two types of bacteria E.coli and P. auriginosa and their organic content can be completely photo mineralized by direct solar light in 60 min. Only few residues of cell wall fragments were not completely photo-degraded. This work also showed that how the sensitized nano–sized particles of ZnO with dye molecules of anthocyanin can be used as a catalyst in killing and photo degradation of gram negative bacteria E.coli in water. The naked ZnO particles degraded up to 83% of the bacteria under solar light (UV and visible), whereas the anthocyanin dye-sensitized particles increased the bacterial degradation by 10 %. Using a cut–off filter, the naked ZnO caused only 40 % bacterial death while the sensitized ZnO particles caused higher than 90 % bacterial complete mineralization. The recovered catalyst reached 90% catalytic activity of fresh catalyst. However, recovered catalyst activity can be totally regained by re-sensitizing it with the anthocyanin dye. The effects of different factors, such as reaction temperature, pH, bacterial concentration and catalyst amount together with nutrient broth and saline media, will be discussed together with the role of the sensitizer.