Installation and maintenance of flow gauging stations to assess wastewater dilution in small creeks is expensive. The method outlined in this paper provides a flexible and cheap alternative for situations with dilution factors smaller than 10 and unambiguous flow direction. It is shown that conductivity profiles from three sampling locations enable accurate identification of the dilution factor with an uncertainty of +/-10-30%. Furthermore, much insight can be gained on the temporal behavior of both, the receiving water and the wastewater treatment system by combined analysis of conductivity and temperature data. In this case study the data also enabled identification and tracking down of illegal polluters.