With technological advances, Cyber-Physical Systems (CPS), specifically critical infrastructures, have become strongly connected. Their exposure to cyber adversaries is higher than ever. The number of cyber-attacks perpetrated against critical infrastructure is growing in number and sophistication. The protection of such complex systems became of paramount importance. Resilience applied to critical infrastructures aims at protecting these vital systems from cyber-attacks and making them continue to deliver a certain level of performance, even when attacks occur. In this work, we explore new advances related to cyber-resilience applied to CPSs. We also explore the use of a metric to quantify the resilience of critical infrastructures. As a use case, we consider a water treatment system.