Recent amendments to the Safe Drinking Water Act have increased the number and scope of activities associated with the regulatory process in drinking water. Computer modeling has become vital to the Drinking Water Research Division in order to fulfill its mission of evaluating technologies, part of the maximum contaminant level development process under the Safe Drinking Water Act Amendments. Water supply related models are presented. The paper concludes that while modeling can be very valuable it must be appropriate and that models must be field evaluated before they are applied in a regulatory context.