Up to half the population of some states in the United States drink water from small systems not regulated by the Safe Drinking Water Act. The quality of the drinking water from these systems is generally unknown and may be suspect. In many jurisdictions, private wells are the primary source of water. In some instances, construction of wells may have met regulatory requirements but may not have adequately prevented disease transmission. Anecdotal information, periodic water-borne outbreaks, and recent well surveys suggest that there are public health concerns associated with these and similar systems. This article provides an assessment of the need for governmental oversight (regulatory and non-regulatory) of drinking water supplies, describes how a "systems-based" approach might be used to evaluate water supply systems and to identify and prevent possible contamination, and presents case studies describing the systems-based approach as well as a comprehensive approach to environmental health that includes drinking water regulation.