The application of the fuzzy logic for determination and assessment of the chemical quality of groundwater for drinking purposes in the city of Zrenjanin is presented. The degree of certainty and uncertainties are one of the problems in the most commonly used methods for assessing the water quality. Fuzzy logic can successfully handle these problems. Evaluation of fuzzy model was carried out on the samples from two representative wells that are located at depths of two aquifers from which water is taken to supply the population as drinking water. The samples were analyzed on 8 different chemical water quality parameters. In the research arsenic concentration (As3+, As5+) is considered as the dominant parameter due to its suspecting carcinogenic effects on human health. This type of research is for the first time conducted in the city of Zrenjanin, middle Banat region. [Projekat Ministarstva nauke Republike Srbije, br. MNTR174009 i br. TR34014]