Groundwater usage characterization in a tribal stretch infected with chronic kidney disease of unknown etiology (CKDu).

This reconnaissance study was carried out in urgency as residents complained of groundwater contamination in a tribal stretch infected with chronic kidney disease of unknown etiology in central India where at least 100 people have already died and more than 300 hospitalized. Multi-indexing techniques were used to evaluate groundwater quality for drinking, irrigation, and industrial purposes. The comprehensive water quality index (CWQI) classifies ∼52 % of the 27 collected samples suitable for drinking, and ∼37 % partially suitable pending certain treatment. While the relative abundance of chemical parameters stands at Ca2+ > Na+ > Mg2+ > K+ for cations and HCO3- > Cl- > NO3- > SO42- > F- for anions, the groundwater in the area suffers from general hardness, nitrate, and fluoride contamination. It is hypothesized that fluoride ions possibly couple with excess alkaline earth elements and anions to form metal-complexes inviting Hofmeister phenomena to act in the human kidneys through ingested groundwater. For agricultural water quality assessment, historically developed 10 irrigation indices have been used that classify most groundwater samples suitable for agriculture. Corrosivity indices reveal that the groundwater has moderate to high corrosive affinity. Although the results of the irrigation and corrosivity indices are coherent with CWQI water classes, the use of so many indices based on certain chemical parameters to evaluate water samples for agricultural purposes delivers mixed results and confuses workers about the actual water quality in the field. This calls for the development of a new, robust, and comprehensive standard for appraisal of irrigation water quality that could be used uniformly worldwide.