In the thesis, we present the results of the bacteriological analysis of five mineral waters and five well waters. Samples have been collected three times from Gyergyóújfalu. The selected non-bottled mineral- and well waters are widely consumed by local people. Beside the general analysis we followed the surviving of the fecal coliforms, Escherichia coli, fecal streptococci and Pseudomonas in the original water samples incubated at 4°C. The microbiological quality of the majority of the analysed well waters and boron waters is not acceptable, which can be attributed to the absence of canalization and the poor hygienic conditions of the environment in certain places.