This chapter examines the transformation of water security from a technical service-oriented framework to a governance-based paradigm grounded in risk management under conditions of uncertainty. Traditionally defined through infrastructure capacity, service continuity, and compliance with quality standards, water security has increasingly become insufficient in addressing contemporary challenges such as climate change, hydrological variability, water stress, and institutional fragmentation. Drawing on the international literature on risk governance, adaptive governance, resilience, precautionary approaches, and anticipatory governance, the study argues that risk-based water security approaches extend beyond technical safety tools and function as governance instruments. These approaches reshape decision-making logics, redefine institutional roles, and transform policy instruments by prioritising uncertainty management, institutional coordination, and long-term resilience. Methodologically, the study is based on a theoretical review of international policy frameworks and academic literature. It demonstrates that the evolution of water security constitutes a structural transformation across three dimensions: decision-making processes, institutional arrangements, and governance instruments. The study concludes that water security should be conceptualised not as an infrastructure performance outcome, but as a governance capacity defined by the ability to anticipate, prioritise, and manage risks under uncertainty. In doing so, it contributes to repositioning risk-based approaches from technical management tools to a comprehensive governance transformation framework in water management.