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In the recent times, multi-metal co-contamination in the groundwater of various parts of the globe has emerged as a challenging environmental health problems. While arsenic (As) has been reported with high fluoride and at times with uranium; and Cr & Pb are also found in aquifers under high anthropogenic impacts. The present work probably for the first time traces the As–Cr–Pb co-contamination in the pristine aquifers of a hilly terrain that are under relatively less stress from the anthropogenic activities. Based on the analyses of twenty-two (n = 22) groundwater (GW) samples and six (n = 6) sediment samples, it was found that Cr being leached from the natural sources as evident from 100% of samples with dissolve Cr exceeding the prescribed drinking water limit. Generic plots suggests rock-water interaction as the major hydrogeological processes with mixed Ca2+-Na+-HCO 3 - type water. Wide range of pH suggests localized human interferences, as well as indicative of both calcite and silicate weathering processes. In general water samples were found high only with Cr and Fe, however all sediment samples were found to contain As–Cr–Pb. This implies that the groundwater is under-risk of co-contamination of highly toxic trio of As–Cr–Pb. Multivariate analyses indicate that the changing pH as the causative factor for Cr leaching into the groundwater. This is a new finding for a pristine hilly aquifers, and we suspect such condition may also be present in other parts of globe, and thus precautionary investigations are needed to prevent this catastrophic situation to arise, and to alert the community in advance. [Display omitted] • We trace the As–Cr–Pb co-contamination in the pristine aquifers of a hilly terrain. • Wide range of pH suggests localized human interferences, calcite and silicate weathering. • Groundwater had high Cr and Fe, however all sediment samples contained As–Cr–Pb. • Groundwater is under-risk of co-contamination of highly toxic trio of As–Cr–Pb. • Precautionary investigations are needed to prevent this catastrophic situation to arise. [ABSTRACT FROM AUTHOR]