Groundwater is the main source of water supply in arid and semi-arid regions. The underground water in these areas is exposed to various types of pollution, such as sewage pollution, use of chemical and animal fertilizers, and industrial sewage pollution. In these areas, identifying polluted waters and managing them, as well as preventing them from becoming more polluted, are of great importance. The management of these waters causes conflicts between society, scientific centers and governments. It should be done by choosing the best option among the available options rather than choosing the best solution. The use of mathematics in carrying out projects in which quality or qualitative parameters are involved makes researchers have a broader and clearer view of the topics. Therefore, fuzzy logic has been highly regarded for decision-making and also for categorizing qualitative parameters. Fuzzy system can be implemented using Matlab software. Complexity and ambiguity in examining the desirability of underground water quality can be properly analyzed by the fuzzy method. Mamdani method is used in this book; this method has 4 basic steps.