In developing countries, due to the Jack of money, drinking water is scarce. Diarrheal epidemics, caused by consumption of unsafe drinking water can be lethal. That is why an alternative approach self-sustaining have been proposed and tested in the field. A simple method, called SODIS (for Solar Disinfection), has been developed to disinfect drinking water. It is proved that a synergic effect of UV-A radiation and temperature can inactivate pathogens causing diarrhea. Up to now, most of the experiments, mainly aimed at developing and improving the methodology. Most of experiments use cells in exponential growth phase for disinfection experiments. But bacteria are more resistant in stationary phase and we found that sensitivity of cells to UV and temperature strongly depends on their growth state. Several experiments with different pathogenic enterobacteria have been conducted in the laboratory and the field to investigate the sensitivity and the behaviour of cells. Now, we know the range of sensitivity at different temperatures for pathogenic strains and the range of UV dose of the sun necessary to inactivate cells. We studied physiological as well as genetic changes in response to SODIS treatment. Some preliminary experiments about regrowth and recovery after treatment have been carried out. These first results revealed that no regrowth or recovery was observed after 48h. It is known that bacteria produce reactive oxygen species (ROS) (OH", 0 2·, Oi , H10 2) in stress conditions. Therefore, they have developed ways for quenching ROS. Enzymes involved in the detoxification of ROS are superoxide dismutase, peroxide and catalase. Activity of catalase has been measured and catalase was observed to play a role in the response. But experiments with mutants of E. coli exposed to the sunlight demonstrated a minor role in protection against UV radiation damage. To know which ways are involved in the mechanism of inactivation, we used mutants of E. coli and we have shown that RpoS, the "starvation" sigma factor, is very important in response against the sunlight. To compare cells exposed and no stress cells, a gene array will be done.