South Cotabato Province located in the southernmost part of the Philippines is one of the country's major food producers. With its agricultural development and increasing population, the health of soil and water resources is at risk. As water is the most important component in agricultural production and in households especially for drinking, evaluating the quality of the water resources is important. Hence, this study aims to determine the suitability of water sources for drinking in South Cotabato Province using on-site water quality testing instruments. A150 sampling points from various water sources namely; deep wells, pitcher pumps, artesian wells, and springs were studied. Ten contaminant parameters were considered, i.e., electrical conductivity, hardness, pH, total dissolved solids, total suspended solids, turbidity, nitrate, phosphate, mercury, and Escherichia coli bacteria. Results showed that 53.33% of the total sampling sources are suitable while 46.67% are not. It also showed that the pitcher pump is the most susceptible to contamination, revealing that 70.45% of the total pitcher pump sources are not suitable. Major contaminants found were mercury, turbidity, and phosphate. The result also revealed that 92% of the sampling sites are within the agricultural area and 50% of the sources are not suitable as potable water. Using the test results, a water suitability map was produced using geographic information systems (GIS). The resulting GIS maps can be useful for policymaking and regulation regarding the utilization of land and water resources in the province. Regular monitoring of the water sources in South Cotabato is recommended to ensure the safety of the people consuming the water.