Potable water distribution systems (WDS) require upgrade strategies based on a pre-defined time interval which is identified by the responsible water authorities. The main goal of a potable water system upgrade is maintaining the standard and acceptable level of service after the occurrence of increases in the serviced population, asset ageing, and/or development of the serviced area. Defining the level of service varies by location according to the codes and regulations adopted by the water authority. In general, two main factors are notable in planning of WDS upgrade strategies: (1) the ‘level of service’ and (2) the ‘upgrade cost’. In the presented paper, a new index has been introduced to evaluate the level of service for WDS from a pressure point of view. The new index that is presented in this paper is named the ‘Pressure Index (PI)’, and incorporates a number of water connections for five different pressure regimes. As a case study, three existing water network systems in the Castlemaine township area, located in central Victoria, Australia, have been investigated and the relationship between the ‘upgrade costs’ and improvement in PI factors is presented.