The water quality of streams and agricultural wells in the Han River basin was studied to see how different farming practices affect it. Samples were taken from areas with highland agriculture, upland and paddy farming, and intensive farming in plastic film houses. Nitrate and phosphorus levels were often too high, especially in the intensive farming area. Heavy metals were mostly not found, except in one specific case. The water was generally okay for irrigation, but the high nitrate levels in the intensive farming area need special attention. A model was suggested to help manage fertilizer and water quality for irrigation.