An understanding of the diversity of community water systems (CWS) in the United States is essential when evaluating the financial implications of the 1986 and subsequent amendments to the Safe Drinking Water Act (SDWA). This diversity, in terms of size, primary water source, ownership, and existing levels of treatment, shape the nature of the technical, institutional, and financial issues that must be confronted in moving these systems toward compliance with SDWA regulations. This report provides a descriptive summary of these operating and design characteristics ofCWS's across the country. The data are organized to help provide a typology of representative public water systems that can be examined to better understand the regional effects of policy implementation. The focus of the analysis is on small water systems, those most burdened by the expanded montoring and treatment regulations; much of the data are also provided for larger systems for purposes of comparison and completeness. Emphasis is directed towards current water treatment objectives being pursued by CWS's and the treatment processes already in place. It is for those smaller systems that may require the addition of multiple water treatment processes that the financial implications are likely to be most severe. As would be expected, there is a shortfall between the number of systems serving fewer than 10,000 people employing multiple treatment processes and the estimated number required. There are systems, however, that have demonstrated success with a number of multiple treatment processes, particularly in the small and medium-size categories. The experience gained by these systems would seem invaluable in efforts to accelerate the process of field testing and approval of technologies applicable to systems serving lower population levels.