Sustainability of industrial systems depends largely on the availability of fresh water. Therefore, the scarcity of this resource has led to the installation of several seawater desalination plants worldwide. The dependability and criticality of these plants increases the demands for systems' availability and reliability. An important intrinsic characteristic of these plants is their capacity to react robustly to shocks and to recover their operation in the face of any type of disruptive event. Resilience, therefore, is a first-order metric that must be present in every maintenance-related decision-making process. Different resilience assessment methods have been applied to various engineering systems and networks. Nevertheless, no quantitative assessment of the resilience in seawater desalination plants has been reported in the literature so far. This work proposes the adaptation and application of an availability-based resilience index using reliability block diagrams and Montecarlo simulations experiments. Besides, an application study in an actual seawater desalinization plant is provided. The main results of this work point to that different maintenance strategies cause different impact in system's availability, and that the definition of such strategies could be made considering their impact on system's resilience.