The relationship between landform class and drinking water quality based on content of inorganic components shows that drinking water quality based on content of inorganic components is high in the stream, valleys, upland drainages, and local ridge classes, and low in the plain small and midslope classes. In fact we can predict water quality using extraction of landform class from a DEM by the TPI method, so that stream, valleys, upland drainages, and local ridge classes have more water quality.