This article illustrates how the 1986 amendments to the Safe Drinking Water Act may affect small water systems by focusing on three small utilities that use groundwater as the sole source of supply. One of these, Mountain Water Company in Montana, faces the possibility of having one of its water sources redesignated as a surface source–a potentially expensive prospect. The problem of another utility, in Vandenberg Village, Calif., involves meeting the expected lower maximum contaminant level for total trihalomethanes. The third utility, Santa Paula (Calif.) Water Works, may require no changes as a result of the new regulations. By carefully studying potential compliance problems, small systems can plan for cost-effective projects where they are likely to be needed.