Wastewater pipeline construction projects, like any other public utility projects, are susceptible to delays, and the Kingdom of Saudi Arabia (KSA) is no exception. In many cases, such delays cause environmental issues and affect commuters, local businesses, project cost, and the public and workers' health and safety. There is a growing need to identify and study the relative significance of the major causes of delays in wastewater pipeline construction projects in the KSA. A questionnaire survey was conducted to assess the importance of 30 potential delay causes based on the perceptions of a select sample of clients, consultants, and contractors. These 30 potential delay factors corresponded to eight main delay categories. The survey data was analyzed using the relative importance index and was then further examined for agreement between the three groups. The top five delay causes identified were labor supply, equipment availability and failure, unforeseen ground conditions, labor productivity, and improper planning. The analysis showed disagreements between clients and contractors as well as between consultants and contractors with regard to the rankings of both individual delay causes and factor categories. The results of this survey will be used in future work to develop decision support systems for wastewater pipeline construction projects. It is anticipated that altogether these studies will contribute to improving the sustainability of wastewater pipeline construction projects in the future.