This study is accomplished to analyze the critical success factors for Knowledge Management Implementing in Urban Water and Wastewater Companies. First, among a large number of critical success factors of knowledge management, nine factors as the main factors are chosen and studied in this paper. After the confirmation of the indices by experts, prepared questionnaire to rank and determine the relations between the related components, was distributed among professionals. Using an ISM-DEMATEL approach, a structural model was formed and then the causal relationships between the factors were mapped out by the interaction-effect diagram. The analysis results show that the factors studied, strategies and objectives, the greatest impact on the success of the implementation of knowledge management in municipal water and wastewater companies will be. The author's proposed model for implementing KM is based on the results of studying the current status of the studied population. This research provides valuable information that hopes to help the KMs work effectively in this business sector. It also provides a solution for the effective development of knowledge management step by step.