Although industrial discharges from point sources are regulated by the Federal Water Pollution Control Acts, National Pollutant Discharge Elimination System (NPDES), some toxic pollutants continue to be discharged into surface waters. Frequently these same surface waters are major sources of drinking water. The Safe Drinking Water Act Amendments have specified a large number of new contaminant levels, (MCLs) at the microgram per liter level. It is possible that many water utilities finding that these new MCLs are violated will seek to identify upstream dischargers and request that regulatory agencies force them to install discharge controls rather than pay for expensive water treatment processes. The study reported in the paper documents the development of a data base management system and a water quality modeling approach that allows drinking water utilities to assess the impact of these upstream discharges on raw water quality. The report makes recommendations to USEPA for modifying its NPDES procedures.