Recent extreme weather conditions have brought flooding threats to Hong Kong, China, due to storm surges and overtopping waves. Since April 2019, the Drainage Services Department (DSD) of the government of Hong Kong Special Administrative Region of the People’s Republic of China has collaborated with the Electrical and Mechanical Services Department (EMSD) to install Internet of Things (IoT) sensors and develop the “Smart Drainage – Flood Monitoring System”, which runs on a native open platform - Government Wide IoT Network (GWIN) and is built in compliance with industrial open standard Long Range Wide Area Network (LoRaWAN) for consolidating and processing data collected. New types of IoT sensors could be quickly installed in areas susceptible to flooding so that DSD could monitor real-time changes in sea and water levels to apprehend possible flooding risks in advance, such that inter-departmental emergency measures could be carried out in a timely manner to protect life and property.