| Summary: | © 2018 American Society of Civil Engineers. The expected final budgeted costs of infrastructure assets are often exceeded during project delivery. Being able to determine the likelihood of changes to the final budget can enable clients to implement strategies to manage and control costs during construction. To understand the changing nature of costs, this paper examines the cost profiles of 1,093 water infrastructure projects that were delivered by a water utility company. Cost overruns were experienced in 656 projects. Only 1 project was delivered on budget; the remaining 436 were completed under final budget approval. A mean cost overrun and underrun of + 19.97 and -32%, are found, respectively. The best-fit distribution for cost overruns and underruns for determining their probability of occurrence is calculated. The research moves beyond examining the cost performance of heterogeneous data sets that have dominated previous studies to the use of a homogeneous sample, which enables more-reliable contingency forecasts to be determined.
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