This study aimed to design a mentoring model for managers in Khorasan Razavi Regional Water Company. In terms of purpose, this research is applied-developmental and was conducted using an exploratory mixed-methods (qualitative-quantitative) approach. In the qualitative phase, the statistical population comprised 12 managers, experts, and human resource specialists from Khorasan Razavi Regional Water Company, selected through purposeful and snowball sampling methods. To validate the qualitative model, the Fuzzy Delphi method was employed with the participation of 10 experts, confirming high validity and expert consensus on the identified components. In the quantitative phase, the statistical population consisted of all 255 employees of the company; due to the limited population size, a census method was applied, resulting in 245 fully completed and analyzable questionnaires. Data collection tools included semi-structured interviews and a researcher-made questionnaire. For data analysis, thematic analysis and Partial Least Squares Structural Equation Modeling (PLS-SEM) were utilized. The qualitative findings yielded 87 initial codes and 13 sub-categories, which were organized into 4 main categories: “Mentoring Infrastructure and Planning,” “Mentor Roles and Interactions,” “Learning and Developmental Processes,” and “Outcomes and Value Creation.” The quantitative results revealed that the effectiveness of mentoring in public organizations depends on focusing on experiential learning, constructive mentor-mentee interaction, organizational support, and structured sessions. The final model can serve as an operational framework to enhance managerial competencies, facilitate tacit knowledge transfer, foster a learning culture, and improve decision-making processes in public sector organizations.