Toxic Screening Models, as described in this paper, provide an approach for identifying and assessing the pollutants that are likely to be present in surface waters used as water supplies. Specific uses of these models include the following: identification and assessment of communities whose water supplies could be vulnerable to synthetic organics resulting from industrial and municipal discharges, or urban and agricultural runoff, design and implementation of a water quality monitoring program, and other water resource planning efforts requiring information on the water quality of surface waters.