Supplying good quality water is an important requirement for the water authority in the West Bank of Palestine. This is due to the impact of the quality of water on public health. As a result of the increasing risks of pollution threatening vital wells field. This research is aiming to develop a decision support system (DSS) for the evaluation of water quality using the water quality index (WQI) technique. We implemented a graphical user interface that allows users to select the physiochemical and micro-biological quality parameters of the tested sample from four basic connections namely; 1) Shufat, 2) EinSamia Wells, 3) Ramallah, and 4) Hezma. Then the test results values are fed into a KNN model that predicts the water class (excellent, good, fair, poor, very poor, and unfit to be used). Based on the water class it can be determined directly if the water can be used for the human to drink or if it can be used for other purposes such as irrigation and industry.