The frequent occurrence of manganese (Mn) at elevated concentrations in groundwater adds a new dimension to the already precarious safe water supply scenario in the alluvial plains and deltas of South Asia (SA). An essential micronutrient, Mn may co-occur with iron (Fe) and/or arsenic (As) and can impart a color, odor, or taste to the water at concentrations of >0.02 mg/L. (1) Adverse effects on neurological development of children from prolonged exposure to Mn in water (∼0.1 mg/L) have been documented (1,2) (also see Table SI-1). Currently, awareness of Mn among scientists, policy actors, and exposed communities remains low. Despite the growing evidence that Mn in drinking water needs close attention and regular monitoring to avoid excessive intake, in 2011 the World Health Organization (WHO) discontinued the health-based value (HbV) of 0.4 mg/L Mn in drinking water. (3) Subsequently in 2021, as part of the second addendum to the fourth Guidelines for drinking-water quality (GDWQ), WHO established a new provisional guideline value (pGV) of 0.08 mg/L. (1) Millions of people in SA are already exposed to Mn above the WHO’s former health-based value (HbV) of 0.4 mg/L. If wells with Mn concentrations above the pGV are considered, then the population exposed to unsafe water would increase significantly.