This data set consists of water chemistry data from streams, wells, rainwater, and canopy throughfall samples. The field measurements were carried out at Rancho Grande in the Brazilian state of Rondonia, in the southwestern Brazilian Amazon basin, at two adjacent watersheds, a forest (1.37 ha), and pasture (0.73 ha). Samples were collected during one entire rainy season starting in August 2004 and ending in April 2005. There is one comma-delimited data file with this data set.