Arsenic is a widespread contaminant of drinking and groundwaters in the world. Even if these contaminations have a geogenic origin, they often are exacerbated by anthropogenic activities. This is particularly true for the Bengal delta. Millions of people in Bangladesh are consuming drinking water with arsenic concentrations ≥ 50 µg/L. Their drinking water supply is based on groundwaters extracted by pumping wells, which were part of a well-drilling program by the United Nations. The intention was to provide the people with groundwater instead of surface water due to its critical hygienic conditions. Unfortunately, many wells extract the groundwater at depths where arsenic concentrations are highest. Arsenic is being dissolved from the aquifer by biogeochemical processes that are fueled by the presence of high amounts of organics in the Bengal delta sediments. This problem was not encountered at the time due to a lack of chemical analyses of the waters.