The Safe Drinking Water Act and its Amendments has focused interest on the factors that cause the deterioration of water between the treatment plant and the consumer. The distribution system itself can contribute to this deterioration. Numerous examples of waterborne disease outbreaks have demonstrated the importance of the distribution system in preventing disease. Water-quality propagation models can be used to study the factors that contribute to water quality deterioration. These models have been used in many locations to study contaminant propagation. The paper describes the application of contaminant propagation models in the South Central Connecticut Regional Water Authority (USA). The fluoride feed was cut off at the water treatment plant to calibrate the model and determine residence times in the system. An extensive simulation of the system was conducted to predict conservative contaminant propagation and chlorine decay. After completing the simulation study a sampling program was conducted to verify the results from the model. In general the field results verified the model predictions. Water quality varied widely over the service area. Long retention times in storage tanks and pipe wall demand, especially in dead end sections, caused significant losses in chlorine residuals.