Spatial distribution and statistical evaluation of pond water quality across 41 wards in Chattogram City, Bangladesh

Surface water (pond) plays an important role in sustaining urban communities, while rapid urbanization in Chattogram City has elevated concerns over its degradation over time. The current research assessed usable pond water quality across all 41 wards in Chattogram City by evaluating key physicochemical and microbial parameters from one representative pond per ward, sampled once during August–September 2025. Using standard laboratory protocols, Pearson correlation, Principal Component Analysis (PCA), Water Quality Index (WQI), and spatial interpolation (IDW), study provides a baseline assessment of the pollution scenario. To the best of our knowledge, this is the first study to use WQI, Pearson correlation, PCA and GIS-based spatial interpolation in a single ward-based comprehensive survey of all 41 wards in a city corporation in Bangladesh to provide a novel city-wide diagnostic baseline for urban pond water quality. Findings showed considerable variability, with DO ranging from 2.1 to 6.3 mg/L and BOD from 1.2 to 12.4 mg/L, whereas nitrate-nitrogen (0.3–4.8 mg/L) and phosphate-phosphorus (0.12–1.42 mg/L) remained moderate. WQI values ranged from 12 to 390, identifying some highly polluted wards (e.g., 2, 7, 21, 24, 32, 41) because of high BOD, phosphate, and low DO. Pearson analysis revealed a very strong DO–BOD correlation ( r = 0.99) and an inverse relationship between DO and fecal coliform ( r = − 0.96), indicating significant organic and microbial pollution, although part of the DO–BOD association reflects the shared measurement basis of the two parameters. Moreover, PCA showed PC1 holding 43.63% of total variance, mostly by BOD, DO, TDS, nitrate, and phosphate, which reflected pollution load as the key controlling factor. These findings demonstrated that wastewater intrusion, surface runoff, and poor sanitation systems were plausible contributors to pond water quality deterioration. The study serves as a one-season, one-pond-per-ward basis, and will provide a baseline water quality monitoring tool, as well as some preliminary baseline-level scientific evidence to help guide pollution control, sanitation planning and sustainable management of surface water in fast-growing urban areas like Chattogram, Bangladesh.