Construction delays are common problems in water supply projects in Ethiopia. The delays inrnconstruction projects are the major causes of project failure. If the delay is not identified and therncorrective project management decision is not taken in time a project may incur extra cost andrnextension of project time, which gives rise to dissatisfaction to all the parties involved andrnnowadays itâ€™s becoming a major obstruction for their development for developing countries likernEthiopia. The research intended to identify the major causes that are led to project delay. Tornachieve the objective, the study employed descriptive research approach and both primary andrnsecondary data were used. Questionnaires and desk review was tools used collect the datarnrequired. This research first identified 58 factors causing delay in Ethiopian water supplyrnconstruction sector, and then the most common and critical causes of construction delay werernevaluated by the data collected in a survey of program managers, regional coordinators and siternengineers. The findings show that the main critical factors that cause construction delays in waterrnsupply sector in Ethiopia are: (1) adverse weather condition, (2) delay in approval of documents,rn(3) equipment Failure, (4) scarcity of material in the market,(5) poor supervision, (6) poor siternmanagement, (7) fluctuation of prices of materials, (8) change in subsurface conditions, (9)rnslowness in decision making process and, (10) low skills of labor.