Based on our last 19 years survey on groundwater arsenic contamination in Ganga-Meghna-Brahmaputra (GMB) plain (an area of 569 749 km2, with a population of over 500 million), we predict a good portion of all the states in Ganga-Brahmaputra plain in India (Uttar Pradesh, Bihar, Jharkhand, West Bengal, Assam) and Bangladesh in Padma-Meghna-Brahmaputra are arsenic affected. Our recent study also indicates out of 7 North-Eastern-Hill states, except Mizoram groundwater of all states are to some extent arsenic contaminated. In last 19 years we analyzed 175 000 hand tubewell water samples for arsenic from all states of India and 50 808 from Bangladesh so far. We undertook medical survey with a group comprising of experienced dermatologists, neurologists, and gynaecologists in the arsenic affected regions of GMB plain. So far our medical team had screened 125 000 individuals from affected villages and registered 9% of them having arsenical skin lesions. So far we have analyzed 60 000 biological samples (hair, nail, urine, and skin scales) collected from arsenic affected villages. In average 80% of samples contain arsenic above the permissible limit in biological samples. Thus many people in affected villages are subclinically affected. Screening around 19 000 children from arsenic affected areas of GMB plain we found nearly 1 100 affected with arsenical skin lesions. Our studies show that children are more vulnerable to arsenical toxicity compared to adults. In these circumstances a successful mitigation strategy should involve safe drinking water supply using all possible sources.