Physicochemical, heavy metal, and microbial risk assessment of harvested rainwater in coastal Koyra Upazila, Bangladesh

ABSTRACT Flowchart showing rainwater contamination from environmental sources leading to Lead, microbial, and heavy metal pollution, resulting in high health risks for vulnerable children. In southwestern coastal Bangladesh, salinity intrusion, tidal surges, and flooding make groundwater unsuitable for drinking, making rainwater a vital source for drinking. This study evaluates physicochemical and microbial quality of harvested rainwater in Koyra Upazila and assesses non-carcinogenic health risks. Contamination levels were evaluated using water quality and heavy metal pollution indices. A total of 93 samples were collected from 31 locations: two from storage tanks for microbial (Fecal Coliform, Total Coliform), physicochemical (pH, TDS, EC, Turbidity), and heavy metal (Pb, Zn, Fe) analyses. Additionally, one sample was collected from each household vessels for microbial analysis only, allowing comparison of microbial quality between storage tanks and household water. Most physicochemical parameters met WHO and Bangladesh standards except turbidity (38.7%) and pH (12.9%). Pb (0.048±0.008 mg/L) exceeded limits in all samples. Fe and Zn were within Bangladesh standards, though Fe exceeded WHO limits in 29.03%. Microbial contamination was higher in household vessels than storage tanks. Heavy Metal Pollution Indices (HPI) and Heavy Metal Evaluation Indices (HEI) indicated slight to moderate contamination due to Pb. Although all non-carcinogenic risk values were below 1, children showed the highest hazard index (0.463–0.985), indicating greater vulnerability. The findings highlight potential health risks and need for regular monitoring and improved household water treatment.