Water management systems play a crucial role in efficiently allocating water resources while taking into account various demands such as agriculture, industry, domestic use, and environmental needs. These systems optimize the distribution of water, ensuring fair access and minimizing water scarcity and conflicts. However, these critical systems are vulnerable to different types of attacks. Depending on the target, these attacks can take the form of physical, cyber, or combined assaults. The protection requirements for water objects, which are integral to critical infrastructure, are primarily defined by legal regulations, technical standards, and other third party requirements. These requirements necessitate the implementation of protective measures. One effective approach to implementing protective measures is through a physical protection system (PPS), which prevents unauthorized individuals from achieving their objectives. The current procedures for protecting these objects can be based on either a qualitative or quantitative approach. In this article, we present a use case that demonstrates a possible method for protecting a specific water reservoir, identified as a national element of critical infrastructure in the Drinking Water Provision subsector. The use case involves analyzing security requirements and designing a PPS for the water reservoir. To assess the effectiveness of the proposed PPS, a quantitative PPS model was developed using specialized software. Additionally, four potential attack scenarios were simulated to verify the functionality of the PPS.