Spatial and temporal assessment of groundwater quality and health risks of Johor state, Malaysia

This study evaluates groundwater quality and potential health risks in Johor state, Malaysia, using dataset obtained from 39 monitoring stations, refined to 28 within the state boundary. The ground water quality index (GWQI) was calculated through parameter weighting, quality rating, and sub-index aggregation, while health risk assessment examined using Chronic Daily Intake (CDI), Hazard Quotient (HQ) approaches. Results showed that GWQI values ranged from 20 (excellent) to 1420 (extremely poor), reflecting substantial spatial variability in groundwater conditions. Approximately 65 % of samples fell within “good” to “moderate” quality (GWQI <100), whereas 35 % were classified as “poor” or worse, highlighting localized contamination issues. Elevated chloride concentrations, reaching up to 4150 mg/L in coastal wells, exceeded both WHO and Malaysian guideline values, indicating saline intrusion risks. In contrast, arsenic concentrations remained below the WHO threshold of 0.01 mg/L across all sites. Health risk analysis demonstrated that the HQ and Hazard Index values for arsenic were consistently <1, suggesting negligible non-carcinogenic risk. However, sites with elevated chloride and phosphate levels may pose indirect risks if groundwater is used for potable use without treatment. Geographic information system (GIS)-based spatial interpolation revealed hotspots of poor groundwater quality in lowland and coastal regions, emphasizing the influence of land use and hydrogeological setting. Overall, the integration of GWQI, health risk assessment, and spatial analysis provides a comprehensive framework for groundwater quality management in Johor state, Malaysia, offering insights for sustainable utilization and regional policy development.