Comparison of the distribution of groundwater remediation units and contaminant (arsenic, iron, fluoride) distribution in Bihar, India for improved water security and management.

Extensive efforts are being made globally to install units to remediate contaminants in groundwaters used for drinking, but are these units being installed in the optimum locations? Here, we explore this question for Bihar, an eastern Indian state with a high reliance on groundwater for drinking water. Bihar is impacted by groundwater quality issues, notably in relation to the geogenic contaminants arsenic (As), iron (Fe) and fluoride (F^-). We map the distribution of groundwater quality remediation units for As, Fe and F^-, and which were implemented from 2016 by the Government of Bihar under the aegis of the Public Health Engineering Department (PHED). The majority of the reported remediation units for As are within a distance of 10 km from the main branch of the River Ganges (Ganga), whereas the remediation units for Fe are exclusively present in the eastern and north-eastern districts of Bihar. All of the remediation units for F^- are located in districts south of the River Ganges. The distributions of the installed remediation units are compared with the distribution and concentration of the target contaminants based on a representative Bihar-wide groundwater sampling campaign reported previously by our group. Inconsistencies are identified in many cases between the distribution of implemented remediation units and areas where elevated levels of the contaminant have been found. Some possible reasons for the apparent mismatches are discussed and include: prioritizing installation on the basis of now out-of-date contaminant distribution maps based on strongly non-representative sampling strategies, and administrative and operational convenience. Our study highlights that there are likely extensive areas in Bihar with groundwater quality issues where necessary interventions are required, but not yet received, whilst there seems to be widespread installation of remediation units where the need is less indicated. Several recommendations are made, including the need for representative, broad-scale (e.g. state-wide) testing to underpin robust decision making for optimal site selection for remediation unit installation for improved drinking water.