Disinfection of water using nanoparticles (NPs) can be achieved through selection of either metals (M) or transition metal oxides (TMO). In this research, 64 formulations of silver-titania nanocomposites (Ag/TiO2) were prepared via a feasible wet-chemistry technique using different natural products as reducing agents. Four selected products successfully reduced Ag(+) ions to Ag, allowing Ag/TiO2 composite to efficiently inactivate microbes found in the activated sludge. The degree of antibacterial activity was measured using zone of inhibition, which indicated all formulations inactivated the bacteria with high potency (0.01 I/6 h). The results from this study and comparison of literature values collectively suggest that light roasted coffee acted as one of the best natural reducing agents due to its low antioxidant index (LAI). Our selection framework also suggested any M/TMO with an oxygen reduction potentials (ORP) range of -0.41 to +1.23 V and any natural product with a LAI (<0.5) would be suitable as a reducing agent. Collectively, the high ORP and low AI provide effective disinfection of water-borne microbes.