Water quality analysis of Sumurup River in Gunungkidul, Indonesia, using the water quality index

Sumurup River is one of the rivers in Gunungkidul, Indonesia, that continuously flows water throughout the year and traverses different land use types. Consequently, it receives numerous waste inputs. Given the limited water resources in the area, it is necessary to assess the water quality regularly. Moreover, this river was previously a drinking water supply, but it can now only be used for purposes with lower requirements, e.g., bathing and washing. The water quality was assessed using three scenarios with different number of parameters in the composite and two indices: the Indonesian Modification of Water Quality Index (INA-WQI) and the Weighted Arithmetic Water Quality Index (WA-WQI). Parameters observed were pH, DO, BOD, COD, NH₃, NO₃, total phosphate, TSS, TDS, and fecal coliform. Results showed that the safe limits of pH, BOD, COD, NH₃, NO₃, total phosphate, TSS, and fecal coliform for drinking water (Class I) were exceeded at several sampling points. In contrast, DO and TDS were below their maximum allowable concentrations at all points. WQI assessment produced varying index values categorized as fair to good (INA-WQI) or excellent to unsuitable for drinking (WA-WQI). Further, the different composite scenarios had a significant effect on WA-WQI but not on INA-WQI scores.