The U.S. Environmental Protection Agency (EPA) has developed this reference guide to assist the operators and managers of small- and medium-sized public water systems. This compilation provides a comprehensive picture of the impact of the water distribution system network on distributed water quality. This reference guide provides information on the following topics: Water supply and distribution process overview Distribution system infrastructure Drinking water regulations Distribution system water quality issues Distribution system monitoring, control and security Operational, financial and management strategies to address distribution system water quality. In addition, to make this document appeal to a diverse group of small system operators and managers, graphical elements such as pictures, tables, blue sidebars, and cartoon illustrations have been used throughout the document. Although every water distribution system is different (in terms of specific layout and operations), all water distribution systems generally have the same components and operate under similar principles and operational strategies. To illustrate solutions to some of the common issues faced by the small community distribution system operators, an example of a small water distribution network (SmallWater, USA) has been included in this document. At the end of many chapters, one or more SmallWater problem scenario(s) are presented along with some guidance on resolving these problems.