An approach to evaluate the relative criticality of different pipes in a water distribution system is presented. To quantify the relative criticality of pipelines, a term "Relative Criticality Index (RCI)" has been defined and measured. RCI was developed by summing up the effects of reliability, cost of break repairs and energy required to repair breaks. These three components have been quantified and added appropriately to obtain an overall criticality index of pipelines in water distribution systems. The model is demonstrated by using a 9.4 square mile area of a water distribution system comprising downtown Phoenix, Arizona. The availability of the study area was estimated to be 46.6 and the relative criticality index indicates that galvanized steel pipes followed by regular steel and ductile iron pipes in the system are critical (i.e. vulnerable) for the system considered. The analysis also presents predicted future costs and energy requirements to repair breaks in the water distribution system for a 20 year analysis period. The results indicate that the expenditures to repair pipe breaks in the system for the analysis period is estimated to be $17.1 million. Additionally, the energy required to repair these breaks during the same timeframe would be 2,486 MWH. A Relative Criticality Index (RCI), along with future requirements of critical resources, should aid cities in better planning and managing of their water distribution systems.