Sinjar plain-northwest Iraq has an abundant amount of groundwater. Due to the importance of this water source, the water quality index (WQI) model was used in the classification of groundwater in the western and eastern regions of Sinjar plain for beneficial use. Groundwater samples were chemically analyzed to calculate the values of WQI. This model consists of a single number of the integrated deviation from standard quality, which indicates the relative importance of each relevant variable for beneficial use. The results indicate that the WQI could be used to determine the particular uses of groundwater. The groundwater in the Sinjar plain is more suitable for irrigation than for livestock drinking and domestic use.