ObjectiveAccurately identifying water intrusion points outside the municipal wastewater network is an important basis for the development of quality and efficiency improvement of wastewater treatment plants (WWTPs). Compared with traditional pipe network investigation method, the internet of things (IOT) technology can quickly lock problem areas and improve wastewater treatment efficiency.MethodsTaking a municipal WWTP in Shanghai as the research object, this paper proposed a real-time monitoring of water quality and quantity based on IOT sensing and a classification diagnosis method for drainage zones, analyzed the water quality changes of main wastewater pipes and branch pipes in the study area, and identified the problem areas with external water intrusion.ResultsThe average influent volume of the WWTPs from February 2021 to June 2022 was 31 082 m³/d, and the maximum daily inflow volume was 1.85 times that of the minimum daily influent volume. By comparing the data of regional water supply and wastewater volume, it can be seen that the actual monthly wastewater volume was always greater than the calculated theoretical wastewater volume, with a difference ranging from 6 725.58 m³/d to 18 107.11 m³/d. The influent volume and water quality of the WWTPs were greatly affected by rainfall. The influent and quality of WWTPs were greatly affected by rainfall. Compared with dry days in non-flood season, the influent rate in rainy season increased by 16.25%, the COD concentration decreased by 14.45%, the ammonia nitrogen concentration decreased by 40.26%, the total phosphorus concentration decreased by 49.84%, and the total nitrogen concentration decreased by 22.56%. The study area was divided into 18 sub-regions of drainage, and water quality online monitoring equipment was installed on the main wastewater trunk pipes and main branch pipes. Among the three main wastewater pipes, during most monitoring periods, the COD quality concentration of the north area trunk pipe was below 100 mg/L, and the phenomenon of external water intrusion was obvious, and the Laozhen District and the Lake District drainage area within the scope of the wastewater pipe network damage led to the mixing of external water into the wastewater pipe network, which was one of the main reasons for the influent BOD₅ concentration of the downstream WWTP to be lower than 100 mg/L.ConclusionThrough the classification method, the detection efficiency of external water intrusion in wastewater network can be improved, the cost of problem tracing in pipe network can be reduced, and the quality and efficiency of WWTP can be improved.