Efficiencies of the series water-soluble anionic and cationic sensitizers have been studied in photodynamic natural water disinfection. It was found that only cationic sensitizers are efficient in photooxidative bacteria killing during photodynamic water treatment. The difference in photodynamic action towards different groups of microorganisms has been observed. The most vulnerable are enterococcus and enterococcus faecalis. Spores of sulfite-reducing clostridium are resistant to photodynamic action but, to provide drinking water, clostridium may be removed by sedimentation and filtration. The dependence of photodisinfection on treatment conditions was studied. It was found that sunlight along with artificial visible light sources may be used for photodynamic water treatment. The photodynamic step, arranged with artificial visible light source, was included in a process of conventional water purification instead of chlorine disinfection. Preliminary pilot testing have shown that photodynamic water disinfection in combination with coagulation, sedimentation, sand and carbon filtrations (latter-to remove sensitizer and products of its photolysis) provides water of high quality, free of bacteria and chemicals as well. (c) 2007 Elsevier B.V. All rights reserved.