In Germany a well-functioning wastewater system has been built up over past decades which has been enabled through constantly high investment. Thus, the investment volume in wastewater treatment in Germany amounts to ca. 4 billion euros per annum. Both the (further) build-up and also the operation and maintenance of the wastewater facilities require, also in the future, considerable funds. Here, the financing of the wastewater treatment system is ensured by the citizens through contributions and charges. Currently, the system is faced with enormous challenges as, despite all the already transacted investments and efforts, investment gaps have occurred and an increasing requirement for rehabilitation in wastewater treatment has arisen. In order to obtain an overview of the current situation in Bavaria, the Chair for Sanitary Environmental Engineering at the Munich Technical University in two cost studies on behalf of the Bavarian State Office the Environment, has surveyed and evaluated the investment and rehabilitation costs with municipal wastewater treatment facilities as well as the condition of the public sewer system in Bavaria. In Part 1 an overview of the project “Investment and rehabilitation costs with municipal wastewater facilities” is given and the approach to and general statistical details of the sewer network from the project “Status of the public sewer system in Bavaria” are presented.