Analyzing Water Main Replacement Policies

Abstract

This paper presents the results of the application of a procedure to assist in planning for the rehabilitation of a water distribution system. The procedure is applied to New York City and incorporates the costs of replacing water mains and those of repairing main breaks to determine least‐cost planning strategies. Results show that New York's current policy of replacing main segments that have had two or more breaks is the least‐cost approach on a city‐wide basis. However, application of slightly different strategies to different pipe diameters and to different boroughs can yield slightly lower costs. Results of the procedure are sensitive to the discount rate and the costs associated with main breaks. Results show that delaying replacement of mains beyond an optimal time yields higher total costs. Several of the results can be generalized and are applicable to distribution • systems of other utilities: (1) Smaller diameter mains should be replaced more frequently, given all other factors are the same; (2) reasonable, least‐cost strategies can be approached even with uncertain input parameter values; (3) knowledge of costs associated with breaks is very important; and (4) in addition to cost, the resulting physical integrity of the system is very important.