Arsenic is a component of groundwater, which becomes toxic for human health when high levels are reached. The most important disease is regional endemic chronic arsenic poisoning. Its long-term effects on health are skin lesions, skin cancer and internal cancers of the bladder, kidney and lung. In Argentina, the central and northern regions, referred to as the Chaco-Pampeana Plain, are the most affected by this disease. Arsenic in groundwater is due to the presence of volcanic ash in the loess sediments of the region. A study case of the impact of arsenic in groundwater on the health of the population in the northeastern Mendoza Province of Argentina is presented here. Preventive measures, including alternative sources, deeper wells, education to raise awareness on health risks, multidisciplinary work and joint actions between health and water managers, are necessary to supply safe water to the population.