We conducted groundwater surveys in the Amazon Basin to determine the occurrence and distribution of arsenic and other contaminants. Initial results indicate that in groundwater resources in the recent floodplains of the Amazon River and of other white-water rivers, arsenic concentrations are often above the WHO-guideline value of 10 µg L−1 for drinking water. We compared the chemical analyses with geospatial data to identify vulnerable areas in the whole region. Understanding the regional geochemical mechanism(s) triggering the enrichment of arsenic in groundwater is important to raise awareness and implement mitigation where needed.