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Arsenic (As) is an important component in thermal springs, which can reach water sources constituting an important hazard for both the environment and people. For this reason, the aim of this paper is to analyze the geologic and geochemical processes that determine the presence and concentration of As in wet-meadows associated to a geothermal field in Patagonia (Argentina) which is used as water supply. To achieve this, during field surveys temperature, pH and electrical conductivity were measured and water and rock samples were taken. Major ions and stable isotopes were determined in water samples while As content was analyzed in both water and rock samples. Due to geological control and chemical analyses, three areas were recognized with respect to major streams in the geothermal field: wet-meadows at headwaters, thermal springs at mid basin and wet-meadows at down basin. Even though, water in wet-meadows have the same origin the obtained results evidence how thermal springs at mid-basin influence the chemistry of these wetlands, particularly those at down basin. In the latter, As raises over two orders of magnitude than the ones at headwaters which surpasses the reference limit, proving that thermal springs are also responsible for the increase of the As content in water changing its quality as a source of potable water. The concentration of this metalloid could be higher but it is retained in travertine and sinter deposits formed near the geothermal discharge area. Understanding processes controlling water quality and the chemistry of As in this type of wetlands is of vital importance, mainly in an arid region where water supply sources are scarce. Unlabelled Image • Water resources in wet-meadows of arid areas of Patagonia • Arsenic contamination of water sources related to thermal springs • Pollution attenuation by arsenic retention in carbonate-silicic geothermal deposits • Geochemical processes were defined based on isotopic and chemical data. [ABSTRACT FROM AUTHOR]