Water Quality Assessment of the São Bartolomeu Stream (Viçosa, Brazil) Using the Water Quality Index (WQI) and Hierarchical Cluster Analysis (HCA): Seasonal Variation and Anthropogenic Influence

Purpose This study assessed the physicochemical and microbiological quality of the São Bartolomeu Stream (Viçosa, Minas Gerais, Brazil) using the Water Quality Index (WQI) and Hierarchical Cluster Analysis (HCA). The aim was to identify spatial and seasonal water quality patterns associated with land use and anthropogenic pressure, including conditions at the drinking-water abstraction point. Methods Water samples were collected at four sites—P1 (rural upstream), C (drinking-water abstraction point), P2 (semi-urban), and P3 (urban downstream)—during the rainy and dry seasons of 2022. Nine parameters were analyzed according to APHA (2017) . The WQI was calculated following IGAM guidelines, and HCA (Ward’s linkage, Euclidean distance) was applied to detect spatial and temporal similarity patterns among sites. Results The WQI ranged from fair to poor, with the intake point (C) showing good water quality in both seasons, while urban sites (P2 and P3) exhibited degraded conditions. HCA revealed two main clusters, distinguishing rural–intake from urbanized sectors, reflecting hydrochemical gradients driven by anthropogenic inputs. Conclusions The combined use of WQI and multivariate analysis provided a robust diagnostic framework for surface water assessment. The drinking-water abstraction point maintained good quality but remains vulnerable to urban expansion, highlighting the need for continuous monitoring and integrated water management strategies.