The presence of pathogens in drinking water supplies is a recurring problem that requires innovative solutions. Solar water disinfection is an example of a point-of-use water treatment scheme that utilizes the natural ability of sunlight to inactivate pathogens. The disinfection process may be accelerated by the addition of simple and inexpensive photosensitizing agents, including riboflavin and its derivative 2′,3′,4′,5′-tetraacetylriboflavin (RTA). Photochemically excited riboflavin and RTA may enhance photoinactivation or target compound degradation by electron transfer or by reacting with molecular oxygen to produce singlet oxygen (1O2). The photostability and 1O2 quantum yield of the sensitizers in the presence of light at circumneutral pH values was characterized. The degradation of selected amino acids, as models for proteins in virus capsids, in the presence of the sensitizers was studied to determine the dominant photosensitizing mechanism and to assess the potential for using riboflavin and RTA to enhance solar water disinfection.