In Hong Kong, the sewage monitoring technology developed by the HKU multidisciplinary team led by Professor Tong Zhang of the Department of Civil Engineering has been incorporated as one of the key components of the control strategy for fighting against COVID-19 since December 2020. The sewage test results have provided a basis for statutory public health action in identifying buildings and places for compulsory testing operations to discover infected individuals. The systematic routine sewage monitoring programme of EPD and DSD now covers over 100 regular sampling sites in Hong Kong, providing early warning signals of COVID-19 re-emergence for over five million people.