Abstract：Chronic exposure to minute amounts of arsenic in drinking water has been shown to adversely affect human health. Over 100 million people, many living in poor areas of the world, are currently exposed to unsafe level of arsenic (> 10μg/L) in drinking water derived from aquifers. Arsenic, sometimes known as the King of Poisons, is a group VA element commonly found as an oxyanion in aqueous environment. Since 2000, testing for arsenic when many countries moved to implement a more stringent drinking water standard of 10μg/L (the WHO recommended safe level for human consumption) has now unequivocally established the world wide occurrence of elevated As in drinking water, especially in ground water. More people are affected by arsenic poisoning in Asia than in the rest of the world combined. The most affected areas are the South and Southeast Asian Arsenic Belt, encompassing the deltas of the Ganges-Brahmaputra-Meghna river and the alluvial fan aquifers in the upstream areas of the Ganga plains, the deltas of the Red river, Mekong river and Irrawaddy river. In China, the alluvial basins of the Yellow River in Inner Mongolia, the Datong and Taiyuan basins of Shanxi, and the Dzungaria basin of Xinjiang produce groundwater rich in arsenic and fluoride, causing arsenicosis and fluorosis. In most sedimentary aquifers, reducing conditions tend to mobilize arsenic from sediment to groundwater, although the detailed processes of hydrological and biogeochemical interactions remain to be fully understood. Cases studies from Bangladesh are used to illustrate that flushing over geological time scales lowers the sediment mobilizable As and organic matter content, resulting in low As groundwater. Such understanding has guided the As mitigation policy in Bangladesh. A worthwhile future research direction is to understand the hydrological, mineralogical, geological and biogeochemical factors that contribute to the sustainable use of low As aquifers in endemic area of As.