Joyce Liu, Carly Barello, Siddhartha Roy , Michael B. Fisher 

Objectives: This study seeks to understand manganese occurrence in drinking water in India.
 
Methods
We searched PubMed, EBSCO Global Health, and Web of Science in December, 2021 and included peer-reviewed studies published after 1969 in English that reported manganese concentrations in drinking water in India (protocol registered with PROSPERO: CRD42024566116). Bias within studies was assessed using methodological quality scores. Regressions and a diagnostic plot were used to assess bias among studies. Results are presented using summary statistics, maps, and estimated populations drinking water exceeding national standards and WHO benchmarks.
 
Results
Extracted data comprised 6,397 observations in 74 studies spanning 59 districts in 24 states. Manganese concentrations ranged from 0 to 12,797 mg/L and were not associated with season or water supply technology (p > 0.05). Overall, 9% of disaggregated data and 21% of aggregated data (95% CI: 9-34%) exceeded the Indian (BIS) national standard for manganese in drinking water (300 mg/L), while 32% of disaggregated data and 58% (40-76%) of aggregated data exceeded the 2022 WHO provisional guideline value of 80 mg/L. Using empirical Bayesian kriging, we estimate nearly 60 million people (95% CI: 45-73m) may be consuming groundwater exceeding BIS standards; over 300 million (281-365m) may be drinking water exceeding WHO provisional guidelines.
 
Discussion
Limitations in this work include variable study quality, dearth of evidence from some states, and low availability of raw study data. Results indicate that a substantive proportion of India’s population may be exposed to manganese in drinking water at levels of potential concern. Such findings could help inform ongoing efforts to achieve universal access to safely managed drinking water for the Indian population.
 
Funding
The authors received no specific funding for this work. Students and staff at the Water Institute at UNC provided in-kind support.