Evaluations of spatio-temporal water quality variability and pollution source apportionment of Lelliso River at Upper Wabi Shebelle river Basin, Ethiopia

The study aimed to assess the suitability of Lelliso River water for drinking and irrigation. The Weighted Arithmetic Water Quality Index (WQI) and Water Pollution Index (WPI) were applied to evaluate its quality. Irrigation suitability was further examined using united state salinity laboratory (USSL) and Wilcox diagrams. Pollution sources were identified through Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA), while health risks were assessed using the Hazard Index (HI). According to the Weighted Arithmetic Water Quality Index (WAWQI), Lelliso River water was unsuitable for drinking (223.8-424.4 in rainy season; 79.6–197 in dry season). For irrigation, quality ranged from good to unsuitable (50.8-157.7 rainy; 51.6-138.9 dry). The Water Pollution Index (WPI) for drinking was 0.69–0.92 (rainy) and 0.74–1.05 (dry), while for irrigation it was 0.38–0.67 (rainy) and 0.49–0.81 (dry). Overall, the river was unsuitable for drinking but safe for irrigation. The USSL diagram confirmed suitability for irrigation, whereas the Wilcox diagram placed all samples in the S3 category, indicating unsuitability. With the highest hazard index (HI = 1.165) at S1 during the rainy season surpassing the acceptable limit, suggesting possible non-carcinogenic risk, health risk assessment revealed ingestion as the predominant exposure channel, especially among children’s. Soil erosion, rock weathering, solid waste disposal, and urban and agricultural runoff were found to be the primary sources of pollution by PCA and HCA. Overall, the river is unfit for drinking, and presents health risks to children due to nitrate.