Mapping the vulnerability of groundwater and assessing the health risks of deficiencies in essential elements in the Lukunga watershed of Kinshasa city

The increasing reliance on boreholes in Kinshasa reflects the ongoing inadequacy of the public water supply, raising concerns about the management of groundwater and the potential health risks connected to aquifer contamination. This study assesses the vulnerability of groundwater in the Lukunga watershed using the GOD method, complemented by a health risk analysis focusing on deficiencies in essential minerals: calcium (Ca) and magnesium (Mg). Hazard quotient (HQd) was applied to evaluate the risk of chronic exposure. Physico-chemical data from 23 water samples (September 2023) supported the generation and validation of vulnerability maps. Integration the GOD model and HQd approach offers a cost-effective and scientifically robust framework, especially suited for data-limited urban settings. The GOD model provided a rapid classification of aquifer sensitivity, while HQd refinement incorporated hydrochemical data to improve exposure risk estimates. The results revealed that nearly 30% of the watershed falls under the ‘very high’ vulnerability category, particularly in downstream areas and along major rivers. The main source of pollution is linked to domestic waste due to poor urban sanitation. Although chemical contamination remains low, the predominant health risk arises from insufficient Ca and Mg levels, with average concentrations of 1.19 mg/L and 1.07 mg/L, respectively. These suggest very soft water and an insufficient daily intake, especially for vulnerable populations. Elevated HQd values indicate potential long-term health consequences, including an increased risk to bone and cardiovascular conditions. This study highlights the urgent need for improved monitoring of groundwater and mineral supplementation strategies to protect public health and ensure the sustainable management of Kinshasa water resources.