An investigation of water quality index and health risks of fluoride and nitrate in the arid groundwater (India)

Groundwater in arid regions such as Northwestern Rajasthan of India is under increasing pressure due to climatic extremes, excessive extraction, and contamination from both geogenic and anthropogenic sources. This study assesses the seasonal dynamics of groundwater quality in Bikaner, focusing on fluoride and nitrate contamination and their implications for drinking suitability and public health. Twenty samples were collected from tube wells during the monsoon (2019) and pre-monsoon (2020) periods and analysed for a suite of physicochemical parameters following standard protocols. Water usability was gauged using several parameters including pH, electrical conductivity, total hardness, total dissolved solids, and ions such as calcium, magnesium, potassium, sodium, bicarbonate, carbonate, chloride, fluoride, nitrate and sulphate, while overall quality was synthesized using the Water Quality Index (WQI). Spatial patterns of contamination were visualized through geostatistical mapping, and hydrochemical facies were interpreted via Piper diagrams. Results revealed that over 65% of pre-monsoon samples surpassed WQI thresholds for safe use, signalling deteriorating groundwater quality. Elevated concentrations of fluoride (up to 5 mg/L) and nitrate (up to 320 mg/L) were commonly detected, with several areas falling into unsuitable categories for drinking. A health risk assessment using the Hazard Index framework found that all demographic groups especially infants were exposed to non-carcinogenic risk, with HI values reaching beyond 12 in critical zones. These findings underscore the urgent need for localized groundwater management strategies in the arid regions where seasonal fluctuations and geogenic factors are intensifying fluoride and nitrate contamination. The spatial clustering of high-risk zones especially in central and southeastern areas suggests persistent vulnerability requiring targeted mitigation. Prioritizing seasonal monitoring, fluoride and nitrate treatment technologies, and community-level interventions to mitigate health hazards and secure water resilience in ecologically fragile region of northwestern Rajasthan.