Water samples collected from eight production wells and eight private residential wells in the Genesee River Basin from September through December 2010 were analyzed to characterize the groundwater quality in the basin. Eight of the wells were completed in sand and gravel aquifers, and eight were finished in bedrock aquifers. Three of the 16 wells were sampled in the first Genesee River Basin study during 2005-2006. Water samples from the 2010 study were analyzed for 147 physiochemical properties and constituents that included major ions, nutrients, trace elements, radionuclides, pesticides, volatile organic compounds (VOCs), and indicator bacteria. Results of the water-quality analyses are presented in tabular form for individual wells, and summary statistics for specific constituents are presented by aquifer type. The results are compared with Federal and New York State drinking-water standards, which typically are identical. The results indicate that groundwater generally is of acceptable quality, although concentrations of the following constituents exceeded current or proposed Federal or New York State drinking-water standards at each of the 16 wells sampled: color (one sample), sodium (three samples), sulfate (three samples), total dissolved solids (four samples), aluminum (one sample), arsenic (two samples), copper (one sample), iron (nine samples), manganese (eight samples), radon-222 (nine samples), and total coliform bacteria (six samples). Existing drinking-water standards for pH, chloride, fluoride, nitrate, nitrite, antimony, barium, beryllium, cadmium, chromium, lead, mercury, selenium, silver, thallium, zinc, gross alpha radioactivity, uranium, fecal coliform, Escherichia coli, and heterotrophic bacteria were not exceeded in any of the samples collected. None of the pesticides and VOCs analyzed exceeded existing drinking-water standards.