One of the challenges in ensuring safe drinking water is to improve its quality from that of raw water to the consumption points. This study assessed the security of a water supply system used by a military base (MB) located on the Rio de Janeiro coast, Brazil. This security was evaluated using two tools: water quality indices (Brazilian and Canadian indices) and structured sanitary inspection. The quality of the water source was classified as “good” according to both indices. However, the water consumed was categorized as “bad” as per the Canadian Index. Sanitary inspection showed weaknesses in the supply system. The MB's drinking water supply system was not safe, presenting a high-level risk and requiring urgent mitigation measures. Therefore, the tools used in this study were found to be suitable for assessing water-supply systems.