The Safe Drinking Water Act (SDWA) of 1974 requires that the U. S. Environmental Protection Agency (USEPA) establish maximum contaminant levels (MCLs) for each contaminant which may have an adverse effect on the health of persons. The SDWA clearly specifies that these MCLs shall be met at the consumers tap. Nevertheless most regulatory concern has been focused on water as it leaves the treatment plant before entering the distribution system. There is, however, growing interest in determining the factors that cause water quality variation in drinking water distribution systems. In order to study the effort, the Drinking Water Research Division of EPA initiated a cooperative agreement with the North Penn Water Authority. The cooperative agreement has resulted in a series of field monitoring and systems modeling studies that lend insight into the movement of contaminants in distribution systems. Previous research has resulted in development of a steady state model the propogation of contaminants in distribution systems. In the paper a more intensive approach is taken to examining the actual pathways of water flow and the time of passage and percentage of water from a given source to a given node in a distribution system. A major finding of the research study is the importance of adequate hydraulic modeling of the systems being studied and the importance of field studies in verifying systems performance. The approach suggested in the research will provide useful insight into the water quality variation that may impact consumers at the tap and the development of monitoring strategies.