Chlorine is the most common type of disinfectant in water supply networks. However, it is a highly unstable oxidizing agent and also known to be consumed in the bulk liquid phase (bulk decay) and at the pipe wall (wall decay). This experimental study was performed for two main purposes: first, to understand bulk decay variation as flow in drinking water supply pipes changes and second, to validate bottle test analysis for measuring chlorine bulk decay. The results indicated that a decrease in the flow rate in a water supply pipe can lead to a decreased bulk decay constant. In addition, the validity of the conventional method of bulk decay constant determination (bottle test analysis) was also confirmed in this study.