<p>Long-term monitoring through the use of water quality indices is essential for identifying trends in water quality, detecting emerging issues, and evaluating the effectiveness of pollution control strategies. In this study, groundwater quality was evaluated for its suitability for drinking purposes, and the Water Quality Index (WQI) was introduced as a practical tool for monitoring water wells in the Zakho District of Duhok Governorate, located in the Kurdistan Region of Iraq. A total of 90 groundwater samples were collected from 15 wells in Zakho during August 2023. The water samples were tested for their major physicochemical properties, including pH, total dissolved salts (TDS), calcium (Ca²⁺), magnesium (Mg²⁺), sodium (Na⁺), potassium (K⁺), chloride (Cl⁻), nitrate (NO₃⁻), sulfate (SO₄^2-), total alkalinity (TA), and total hardness (TH). A weighted arithmetic index was applied using Iraqi standards and other international and national standards to evaluate the overall quality of the water. The results revealed that most parameters were within acceptable limits, with the exception of calcium (Ca²⁺), which exceeded permissible levels in most cases, followed by magnesium (Mg²⁺) in several instances, and total hardness (TH), sulfate (SO₄²⁻), and TDS in a few cases. The calculated WQI values ranged from 40.65 to 70.48, indicating that 60% of the samples were classified as “good” quality, while 40% were categorized as “poor.” Hydro-chemical facies, identified using the Piper diagram, showed that the dominant water types were Ca²⁺ –Mg²⁺ –HCO₃⁻ (80%) and Ca²⁺ –Mg²⁺ –SO₄²⁻ (20%), suggesting that alkaline earth metals predominate over alkali metals. Based on these findings, it can be concluded that some groundwater sources in the study area are unsuitable or excessively hard for direct human consumption, and the implementation of water softening treatments is strongly recommended prior to use.</p>