In terms of infiltration and inflow measurement in sewage works, implementation often depends on a cost-benefit evaluation of causes and fault points identified using television camera monitoring,following by flow measurement to understand the actual state. However, it is often the case that countermeasures may not be carried out because time and money is spent on identification of the broad issues such as improper pipe connections. We implemented our study on the practical use of the investigative method, with a focus on the change in sewage temperature in manholes when infiltration and inflow occurred, as an investigative technology to help measure infiltration and inflow.