In 2007, EPAL – Empresa Portuguesa das Águas Livres, S.A. – started to implement a water safety plan (WSP) in its water supply system, from source to tap, following the international methodologies regarding risk management of water quality. Since the implementation of its first version of the WSP, EPAL has been working on the optimization of its methodology regarding identification and evaluation of hazards/hazardous events and risk assessment. The main objective of this optimization is the prioritization of capital investments and implementation of mitigation actions, within the integrated risk-based management of the company. For this purpose, the initial risk assessment matrixes were optimized with the integration of new specific multicriteria tools to evaluate risks associated with different types of operational assets. The final risk assessment took into account the strategic importance of each individual asset within EPAL's supply system. The new risk assessment methodologies have helped decision-making and prioritization of capital investments and also allowed EPAL to better pinpoint the critical issues to address in its supply system.