This research examines the causes of the failure of water conservation messages in Tehran metropolis and designs an alternative persuasive model. Tehran is experiencing its sixth consecutive year of drought, with reserves in its five supply dams reaching their lowest level in six decades; yet numerous communication campaigns have failed to secure citizen engagement due to the collapse of public trust in water management institutions. The aim is to design a comprehensive, context-specific persuasive messaging model grounded in restoring public trust in water management institutions for managing Tehran's water crisis. The method is qualitative with a thematic analysis approach, conducted through twenty semi-structured in-depth interviews with experts across four domains: water resource management, public relations, crisis management, and sociology. The result includes extraction of 628 initial codes, 87 basic themes, 21 organizing themes, and 6 global themes organized around the core category of "persuasion based on restored trust." The final model operates across four levels: foundational (trust and legitimacy restoration), strategic (evidence-based message design), tactical (multi-channel implementation), and evaluative (monitoring and continuous improvement). This model offers an operational framework emphasizing transparency, honesty, outsourcing messaging to credible local sources, genuine citizen participation, and network smartification, charting a pathway for policymakers to restore trust and enhance acceptance of persuasive messages.