In 2002, a leukemia cluster was identified in the town of Fallon, Nevada, and concerns were raised regarding the occurrence of tungsten in drinking water as a possible contributing factor to the leukemia cluster. Tungsten is found in measurable concentrations in surface waters of the Carson River Basin, and tungsten occurrence is widespread throughout all aquifers of the Carson Desert – the primary source of drinking water in the Fallon area. The purpose of this study was to assess the occurrence and geochemistry of tungsten in the Carson River Basin, and to determine whether the tungsten in drinking water in the Carson Desert was naturally occurring. Three geochemical processes controlling tungsten concentrations in surface water and groundwater in the Carson River Basin were identified: (1) evaporation and transpiration, (2) reduction–oxidation reactions, (3) pH-dependent adsorption–desorption processes, and geothermal processes. An additional finding of some note is elevated polonium-210, which is also naturally occurring. The distribution of tungsten concentrations was consistent with the distribution of geochemical parameters representative of these four predominant geochemical processes, demonstrating that tungsten in groundwater aquifers in the Carson Desert is naturally occurring, and is not attributable to a point source.