To the sewer systems households, industries and other activities are connected. The wastewater is collected at treatment plants where a nutritious sludge is produced. The sludge does not only contain nutrients, but also hazardous substances originating from different activities in society. To reduce the flow of hazardous substances to treatment plants and to create a sustainable recycling of plant nutrients the Swedish Water & Wastewater Association has developed the certificate system REVAQ. This certificate requires a good quality of the sludge but also that the treatment plants maps the origin of the unwanted substances. Uppsala Water and Waste Inc., a municipally owned company that runs Uppsala’s water and wastewater system, just recently got the REVAQ-certificate. The objective of this project was to map the flow of heavy metals to the wastewater treatment plant. To locate the origin of the hazardous substances in Uppsala and to compare the results with a study done 1989, the flow of hazardous substances in the sewage system was measured with two methods, flow proportional measurements which were more expensive and complicated, and passive measurement, which were simpler and cheaper. A comparison between the measurement methods was done in order to be able to use only the passive measurement method at the next sampling session but still be able to get results almost as informative as the more complicated flow proportional method. Also an analysis with SoFi, an Excel tool which identifies origins of hazardous substances in cities, was done. The results from the flow proportional sampling show that the concentrations of lead, mercury and cadmium has been reduced since 1989 while the concentrations of zinc, copper, chromium and nickel has increased in the industrial areas I1 and I2. In the residential areas S5 and Bäcklösa the concentrations of mercury, copper and lead has been reduced since 1989 while the concentrations of cadmium, zinc and chromium had increased. Though, the ratios between the concentrations of metal and phosphorous in these areas, indicate that the concentrations of cadmium and zinc might be too high to come from a residential area. The industrial area I1 was distinguished as the area with the highest concentration of many metals. Even though the concentrations of some metals had increased since 1989, only the flows of chromium, nickel and zinc had increased since 1989. A higher percentage of the flows of cadmium, zinc and silver came from the residential areas compared to the industrial areas. The results from the passive sampling show that the university area Ultuna had the highest concentrations of many metals. The analysis with SoFi indicates, just as the measurements, that the Uppsala Water and Waste Inc. interventions to reduce the flow of cadmium, copper, zinc, chromium and mercury to the wastewater treatment plant Kungsängsverket should be focused on the residential areas rather than the industrial areas. The comparison between the sampling methods showed that there was a linear relationship (p<0.05) between the results of the two sampling methods when a sampling is done for two weeks and at a temperature of 8 ºC. The relationship must be validated before it is used in future samplings.