A nationwide reconnaissance of selected minor elements in water resources of the 50 States and Puerto Rico was made by the U.S. Geological Survey in cooperation with the U.S. Bureau of Sport Fisheries and Wildlife during autumn, 1970. Initiated in response to the growing need for data on minor elements in water, including toxic metals, the synoptic survey provides an up-to-date baseline of such data largely for dry-weather flows of streams that are sources of municipal and industrial water for the Nation's metropolitan areas.