This article presents the development of a decision support system for water pollution in Tigris River (WATER-DSS). This DSS presents several strategies to manage water evaluation and treatment in order to protect human health by building a decision support system to help the authority of water supply stations to find information about water management. This DSS is designed to help address and support multiple water pollution causes and multiple decision makers, in several places in Baghdad. The evaluation of the DSS discusses the effect of water quality index management on the water pollution. The system detects the pollution causes and type and suggests a decision for cleaning the water so that it can be used by human. The application uses a set of (24)water-pollution parameters, specific to the pollution causes, in order to deal with the water pollution accidents and take emergency measures effectively. Tigris River is selected as the case study in this paper. The frame of the water pollution DSS is based on a mathematical model. The results support the primary decision in emergency cases and offer a suggestion to apply a suitable method for treatment the polluted water.