The district of Gunungkidul on Java Island in Indonesia is affected by an acute water shortage, especially during dry seasons. Because of its karst topography, rainfall percolates rapidly into underground caves, limiting surface storage. As a consequence, potential sources of water to supply the local population are rainwater and water derived from underground caves. However, water availability is in most cases insufficient and water quality does not meet the WHO drinking water quality standards. One aim of the Integrated Water Resources Management Indonesia Project was to find, develop and implement an appropriate water treatment in order to ensure a safe drinking water supply to the population of Gunungkidul. A decision-making process was used to select the most appropriate technology and a suitable location for construction. Laboratory experiments were conducted with local materials to assess treatment performance.