A chironomus larvae infested water supply system was studied in detail for detecting its source and remediation. The study covered raw water source, units of water treatment plant, underground water storage reservoir, elevated service reservoir and water distribution pipeline. Since the larvae is the hatching of midge fly, the open ends in the water supply system like water treatment plant, underground storage reservoir, elevated service reservoir were studied first and found to be free from larvae. Finally excavation was carried out at the underground pipeline near the larvae infested tap ends. It was found that some residential units were discharging domestic wastewater just below the ground surface leading to contamination of drinking water. Pipe joints were opened for further study and growth of several species was found inside the pipe. However, the exact location of contamination could not be detected. The closed loop pipeline was opened at one end to scour off any contamination with clean water. After few hours of flushing, the insects were not detected at the consumer ends. This paper describes the systematic methodology that can be adopted for such investigations.