The Chi and Mun River Basins, the primary tributary of the Mekong River Basin in Thailand, is undergoing significant land use changes that impact water quality. Understanding the relationship between land use and water quality is crucial for effective river basin management, providing insights applicable to global water systems. While past studies have examined water quality in the Mekong River Basin, research specifically focusing on the Chi-Mun River Basin remains limited. This study analyzes the spatial and temporal effects of land use changes on water quality from 2007 to 2021 using land use change estimation, 11 water quality parameters, and redundancy analysis (RDA). Water samples were collected in January, March, May, and August across multiple years. Seasonal variations were assessed, with dry season samples from January and March and wet season samples from May and August. Key findings include: (1) pH, Biochemical Oxygen Demand, Total Coliform Bacteria, Fecal Coliform Bacteria, Total Phosphorus, Nitrate Nitrogen, Ammonia-Nitrogen, and Suspended Solids increased during the wet season, while (2) Dissolved Oxygen, Electrical Conductivity, and Water Quality Index were higher in the dry season. (3) Land use changes had a greater impact on water quality during the wet season, driven by increased runoff from expanding urban and agricultural areas and declining paddy and forest cover. (4) Forests and aquatic areas improved water quality, while agricultural and urban expansion contributed to its deterioration. These findings underscore the need for sustainable land management strategies to balance regional development with ecological conservation in the Chi-Mun River Basin.