The aim of this study is to reduce the consumption of contaminated drinking water of a periurban population in Bolivia. Providing information about a simple alternative to clean water before drinking and using different strategies, namely prompts (reminder) and self-commitment (voluntary, public commitment), we studied and tested the effects of these interventions on people's drinking water behavior and habits. One major psychological barrier for people not to carry out a new behavior is their already existing habits contradictory to the new behavior. The implications of this rather general assumption we applied to the problem of contaminated drinking water and the connected drinking water habits in Bolivia. The need to change has arisen from problems that supplied water in Bolivia is microbiological contaminated or in no central drinking water supply system at all. Especially children below 5 years of age are at high risk of diarrhea and infant mortality (acc. to WHO Report 2005 Bolivia 6-7%, compared to Switzerland 0.5%). We concentrated on a simple household level solution, where focus was laid on capacitating people, so they themselves take care of improving their situation. The strategy we promoted is based on the principle of Solar Water Disinfection (SODIS). In short, it means putting a plastic bottle filled with water into the sun for 6 hours and UV-rays and temperature inactivate the microbes. The method used was a 3-point panel questionnaire study with different interventions between the measurements. Investigation was realized in 5 areas in Bolivia, 1 being control area with no intervention. Intervention period in total was 2 months. The panel questionnaire included demographic and social characteristics, current water use, intervention relevant questions and a set of psychological factors. Main analysis focus was the impact of prompts (reminder to use SODIS) and/or public self-commitment (voluntary commitment to use SODIS) in changing the existing behavior. Further analysis was conducted to identify psychological factors (such as intention, attitude, personal health norm, affect, perceived difficulty or cost-benefit-consideration) influencing behavior when being exposed to a certain intervention or not. Results show strong effect of no intervention versus prompt versus prompt and self-commitment in rising use of SODIS over time. For analysis of differences in time and behavior a Multivariate Analysis of Variances was calculated. With the use of a regression model differential influence of the above mentioned psychological factors on behavior were found for the different intervention strategies. One general finding to the field of behavior change is, that simple and non-costly interventions can have more effect than one may suspect. But a lot more important is to understand how those interventions function in terms of influence on psychological factors which in turn determine our behavior. This study has taken an essential step in this direction and the findings will improve effective design of further intervention campaigns.