The water quality index (WQI) is a unified measure that summarizes many water test characteristics to provide a single value indication of water quality. The Tigris River is a vital water source in southeastern Iraq. Monthly water samples were collected from August 2022 to July 2023. Eighteen parameters were analyzed. The p < /ins>Principal cComponent aAnalysis (PCA) was applied of technique to analyze the environmental variables. First, it helped us choose the most significant water quality limits and determine their comparative weights. Second, we constructed excellence curves for the selected parameters to estimate the WQI conclusion based on water quality values. Six variables were selected to be included in the guide based on their significant influence on water quality which involved total dissolved solids (TDS), total hardness (TH), dissolved oxygen (DO), total coliform (TC), chemical oxygen demand (COD) and chlorides (Cl^-), aiming to capture the specific features of the Iraqi waters. In this analysis, an eigenvalue of 8.325 was observed, signifying a substantial value given by the initial fifteen factors examined. The cumulative effect of the three components, namely F1, F2, and F3, amounted to 46.25%, 69.46%, and 79.878%, respectively. The results of the Iraq wWater qQuality iIndex (WQI) for the Tigris River in southeast Iraq revealed acceptability, with scores of 65.32, 53.03, and 57.15 during winter, spring, and autumn, while the summer season exhibited poor water quality with a score of 23.45. On an annual average basis, the water quality of the Tigris River was found to be poor, with a mean of 49.74 ± 18.256. These results suggest that the water in the entire river is unsuitable for potable water.