Modern life and human progress are supported by the operation of critical infrastructure. Although they ensure the well-being of human life, they also present risks that are difficult to manage. These risks are particularly exacerbated when critical infrastructures are interdependent and are maintained by the public and private sectors. Water supply systems are among the most important, yet vulnerable, critical infrastructures in modern society. Safe drinking water is a prerequisite for ensuring public health and human activities, and treated wastewater is essential for the prevention of waterborne diseases and environmental safety. Today, as in the past, the world is witnessing health, economic, environmental, and other problems caused by intentional anthropogenic impacts on water and wastewater facilities. Improving the safety and stability of this critical infrastructure is therefore a national strategic priority for all countries around the world. We present certain historical and current events leading to the disruption of the security of the water and wastewater facilities, especially from hybrid threats. Existing legal standards and current regulations for the protection of critical infrastructures, including the water and wastewater sector, are discussed. Based on our comprehensive analysis of the available data, methodological solutions to modernize the framework for the protection of water and wastewater critical infrastructure are proposed.