The topic of this thesis was water leaks in the sewer network in the city of Varkaus. The purpose of the thesis was to clarify sewer leaks as a field research. The aim of the field research was to obtain detailed information about the leaking spots and the reasons for them, as well as about incorrect connections in the sewer network. The research methods which were used were the visual method, the smoke test method and some in places TV-filming.

The water leakage investigation was carried out in the city of Varkaus because the aim was to find out what is the reason for large amounts of leakage water. The main reasons for the reduction of leakage water are the exceeding of purification capacity at the time of large amount of leakage water and extra cost caused by leakage waters to the city of Varkaus. Wastewater matters are regulated by a number of different laws, such as water management act, water act, environmental protection act and the land use and building act. These laws require the city of Varkaus to reduce leakage water.

The research was started by finding out the amounts of leakage water in the city of Varkaus by comparing the annual maximum and minimum flows. On the basis of this pre-feasibility study the research areas were selected for this leakage water research. Areas to explore were Luttila´s IVO, Kuvansi, Kaura-Aho, Könönpelto and the one part of Käärmeniemi. The field researches were carried out by the visual method and the smoke test method in the summers 2011 and 2012. The research also included the documentation in the electronic form into the network information system.

The result of the leakage water research was an electronic AutoCAD-based network data material and Excel table of the research areas. These two also show the locations and reasons for the leakage and the locations of the incorrect connections. The water leakage investigation data will be used when planning wastewater sewer system renovations.