Solar water disinfection - the SODIS method - is a simple procedure to disinfect drinking water. Contaminated water is filled in a transparent PET-bottle or glass bottle and exposed to the sun for 6 hours. During this time, the UVA radiation of the sun kills enteric bacterial pathogens. The SODIS method helps to prevent diarrhea and thereby is saving lives of people. In this thesis, the disinfection process during SODIS was analyzed with the latest culture-independent methods. Viability indicators suggested that membrane functions play a crucial role during disinfection. The respiratory chain and the F1F0-ATPase were confirmed as primary targets on the way to cell death. Generation of reactive oxygen species (ROS) and protein oxidation are a likely cause for breakdown of the cellular energy metabolism within the first minutes of irradiation. Effects of solar light resemble strongly the effects of oxidative stress and cellular aging.