Water Quality Index: Physicochemical and Microbiological Risk Assessment of Drinking Water in Maya City, Eastern Ethiopia.

Objective: This study aimed to evaluate drinking water quality across different sources and seasons and to develop Water Quality Index (WQI) based on selected physicochemical and microbial parameters in Maya City Administration, Ethiopia.

Methods: Drinking water samples (n=120) were analyzed for microbial and physicochemical analysis. Safety indicator bacteria were detected and counted using petrifilm, while the physicochemical parameters were determined using standard procedures. The WQI was computed following Brown's weighted arithmetic approach.

Results: Nearly 31% of the samples exceeded the Ethiopian standard limit (0/100 mL) set for total coliform, 23% for coliform, and 15% for E. coli. The occurrence of E. coli was significantly higher during the wet season (p = 0.014). The mean microbial WQI score was 24.44, with 35% under the risky category, and seasons showed no effect on WQI. The pH, electrical conductivity, temperature, turbidity, sodium ion, and zinc level were within the acceptable limits of the Ethiopian standard limit. About 93% of the samples were within the acceptable limit set for total dissolved solids. However, Ca²⁺ and total hardness exceeded the acceptable limit in 100% of samples, while Mg²⁺ exceeded the limit in 67.6% of samples. The WQI calculated using physicochemical parameters was within the acceptable category ranging from 2.63-9.26.

Conclusion: Despite the overall WQI shows suitability for drinking, the high occurrence of E. coli and coliform, together with elevated water hardness, remains a public health concern that requires mitigation measures.