The district of Gunung Kidul in Southern Java is one of the poorest regions in Indonesia. It is located above a big karst formation with very poor filtration and low storage capacity, which lead to vulnerable water quality all year round and acute water shortages in the dry season. Deficient waste water treatment combined with fast and direct infiltration into the karst results in high levels of contamination in the groundwater, which is used for drinking. To improve the water quality, a three-step water treatment concept was developed and selected technologies were examined in a field laboratory for their disinfection efficiency under local conditions: chlorination, UV disinfection, and ceramic filtration. The first results suggested that UV disinfection is effective, but might be too vulnerable, that chlorination seemed not to be reliable under local conditions, and that ceramic filtration seemed to be the most efficient technology.