There are many works on resolving delays in disaster communication, which are a critical concern in disaster IoT systems, but some concerns remain. We focus on delays that are derived from the communication architecture of disaster IoT systems, which is composed of both unicast and multicast communications, and propose a smart push notification method for improving delay over third-party push server in disaster IoT systems for detection of water flood during an emergency. The proposed method determines the exact time point to send a push notification and results in improved disaster preparedness. This work implements the proposed method on a third-party push notification server, and the experiment results show that the proposed method with the smart push notification algorithm reduces delay by 20 % and error rate in the expected future measurements by 4 % compared to the legacy methods.