The objective of this research is to study the financial feasibility of construction project of water supply system expansion in Provincial Waterworks Authority, Chiang Mai. This research is quantitative research based on secondary data by using Geometrical method to estimate people in the service area and find 5-years back average since 2558-2562 for predicting water user. In addition, the NPV, BCR and IRR parameters were used to analyze financial feasibility of the project. The results found that the investment in construction expansion of Provincial waterworks Authority in Chiangmai branch increased the production capacity from 6,300 cubic meter per hour (m³/hr) to 13,650 cubic meter per hour (m³/hr) with the total of 3,072.861 millions bath. Furthermore, the study of financial analysis found that this project is not worthwhile for investment due to the NPV is -3,297.6 millions bath, BCR is 0.52 and IRR is 1.45 which less than limited discount rate of the project (7.95).