Predicting groundwater fluoride levels for drinking suitability using machine learning approaches with traditional and fuzzy logic models-based health risk assessment

• Fluoride concentration varies from 0.1 to 3.10 mg/l throughout the study area. • In the study area, the geogenic source plays a key role in fluoride concentration. • The AdaBoost model performs with high accuracy in groundwater fluoride prediction. • Nearly 65% and 12% of samples are at risk for dental and skeletal fluorosis. • In the fuzzy model, all age groups have a very low to moderate risk for dental caries. The primary objective of this study is to measure fluoride levels in groundwater samples using machine learning approaches alongside traditional and fuzzy logic model-based health risk assessment in the hard rock Arjunanadi River basin, South India. Fluoride levels in the study area vary between 0.1 and 3.10 mg/L, with nearly 32 samples exceeding the World Health Organization (WHO) standard of 1.5 mg/L. Hydrogeochemical analyses (Durov and Gibbs) clearly show that the overall water chemistry is primarily influenced by simple dissolution, mixing, and rock-water interactions, indicating that geogenic sources are the predominant contributors to fluoride in the study area. Around 446.5 km 2 is considered at risk. In predictive analysis, five Machine Learning (ML) models were used, with the AdaBoost model performing better than the other models, achieving 96 % accuracy and a 4 % error rate. The Traditional Health Risk Assessment (THRA) results indicate that 65 % of samples pose a highly susceptible for dental fluorosis, while 12 % of samples pose a highly susceptible for skeletal fluorosis in very young age groups. The Fuzzy Inference System (FIS) model effectively manages ambiguity and linguistic factors, which are crucial when addressing health risks linked to groundwater fluoride contamination. In this model, input variables include fluoride concentration, individual age, and ingestion rate, while output variables consist of dental caries risk, dental fluorosis, and skeletal fluorosis. The overall results indicate that increased ingestion rates and prolonged exposure to contaminated water make adults and the elderly vulnerable to dental and skeletal fluorosis, along with very young and young age groups. This study is an essential resource for local authorities, healthcare officials, and communities, aiding in the mitigation of health risks associated with groundwater contamination and enhancing quality of life through improved water management and health risk assessment, aligning with Sustainable Development Goals (SDGs) 3 and 6, thereby contributing to a cleaner and healthier society.