Challenge testing was carried out of full-scale prefiltration and ceramic ultrafiltration (UF) modules in a mobile drinking water treatment system. Three consecutive indirect integrity tests were performed using naturally contaminated public drinking water, stocking with wastewater as well as addition of powdered activated carbon. Besides checking the removal efficiency and integrity of the ceramic UF membrane, the overall aim of this type test was to prove that the treatment system fulfils the stringent limits of the German Drinking Water Regulation. Up to 4-log removal of different bacteria was achieved by the UF module, whereby log removal values (LRV) were only limited by the bacteria numbers in feed. Complete removal was likewise achieved for spiked particles. High integrity of the ceramic membrane proved that the mobile treatment system can not only be used for drinking water supply for disaster relief worldwide but also for emergency municipal water supply in Germany.