This study presents an innovative emergency floor drainage system featuring a passive overflow mechanism inspired by free spillway hydraulics to improve safety and hygiene in townhouse environments. Conventional townhouse drainage systems, often limited to a single outlet, are vulnerable to overflow incidents caused by blockages or extreme weather, potentially causing water damage and sanitary hazards. The proposed system introduces a secondary emergency drain positioned at a higher elevation than the primary drain, activating automatically via gravity when the main drain fails or is overwhelmed. The method was experimentally validated by simulating a primary drain obstruction in a genuine townhouse project in Thu Duc City, Vietnam. According to the results, the emergency drain successfully prevented water from spilling outside the designated area, significantly lowering the possibility of property damage and preserving hygienic conditions without requiring powered components. This research contributes a robust, low-maintenance solution for improving the resilience of residential drainage infrastructure. It advocates for its integration into contemporary townhouse design to mitigate overflow risks and enhance occupant safety.