The quality of groundwater in shallow aquifers impacted by inadequately managed sanitation facilities in coastal Bangladesh

Ensuring access to safe and affordable drinking water remains a core target of the Sustainable Development Goals (SDGs), yet this remains a critical challenge in many developing regions due to inadequate sanitation infrastructure. In Bangladesh, where over 90% of the population relies on groundwater, shallow aquifers are increasingly at risk of contamination from on-site sanitation systems. This study investigates the impacts of pit latrines and septic tanks on groundwater quality in Khulna, a coastal city in southwestern Bangladesh. A total of 40 groundwater samples were collected from 20 tube wells located within 0-6 meters from pit latrines and septic tanks, during both the monsoon and dry seasons. Fifteen physicochemical and microbiological parameters were assessed, including pH, EC, TDS, major ions, total coliforms (TC), fecal coliforms (FC), and Escherichia coli (E. coli). The results indicate widespread contamination across both sanitation types, with more severe impacts observed near pit latrines. Approximately 50–70% of samples exceeded WHO limits for EC, TDS, Na⁺, Cl⁻, and HCO₃⁻, with elevated concentrations more pronounced during the monsoon season. Microbial contamination was found in 80% of tubewells located near pit latrines and in 50% of those near septic tank latrines. The temporal analysis revealed that TC, FC, and E. coli contamination were more prevalent during the monsoon season compared to the dry season. The spatial and temporal analysis revealed that chemical parameters dominate during the dry season, whereas microbial contaminants are more prevalent in the monsoon. The correlation matrix and PCA suggest that microbial contamination likely originates from a common source, with its occurrence in shallow aquifers largely influenced by stormwater infiltration and tubewell depth. Water Quality Index (WQI) assessments classified over 50% of the samples as very poor or unsuitable for drinking, with pit latrine-adjacent wells consistently exhibiting higher health risks. The study concludes that shallow aquifer groundwater in Khulna is unsafe for consumption without treatment and recommends urgent measures, including improved sanitation design, regular water quality monitoring, and the development of alternative safe water sources. These findings offer critical baseline data for policymakers aiming to reduce waterborne health risks in coastal Bangladesh.