scope:

Introduction

A drinking water distribution system is a system of pipes that carry potable water from treatment plants or water sources to consumers. It is also the last barrier available to water systems to maintain safe and high-quality water. This manual presents typical distribution system water quality challenges, providing summaries of typical responses and best practices as a "first stop" for drinking water system professionals.

Since each distribution system is unique, this manual is not intended to be all inclusive. Rather, it is a guide that summarizes the issues and actions to be taken when distribution system issues arise and provides references to other industry standards and publications that provide more detail. Additionally, this manual does not delve into treatment process or source water changes that can affect the quality of water that enters the distribution system. Readers are encouraged to familiarize themselves with the American Water Works Association (AWWA) standards and manuals of practice related to water source and treatment. These manuals are available for purchase online at http://www. awwa.org/publications/manuals-of-practice.aspx (accessed May 16, 2016).

For purposes of this manual, distribution systems include pump stations, ground and elevated storage tanks, potable water mains, potable water service lines, and all associated valves, fittings, and meters. Potable water customer service lines are excluded (Texas Commission on Environmental Quality 2015).

The chapters in this manual are organized based on the most common distribution system challenges that water systems face today. These are listed in Table 1-1.

Each chapter provides an introduction and description of a Distribution System Water Quality (DSWQ) Challenge, followed by:

• Discussion and description of the factors associated with each challenge. See text box(es) in each chapter for a summary of Characterizing the DSWQ Challenge;

• Summaries of available response actions. See text box(es) in each chapter for a summary of Responding to the DSWQ Challenge; and

• Recommended best practices for optimizing DSWQ. See the table in each chapter that lists DSWQ Best Practices, which are rated as "basic" or "advanced." Some chapters include specific definitions for these terms. Generally, basic practices are the actions all water systems should perform if they have experienced the DSWQ challenge noted. Advanced practices are for water systems that wish to optimize and/or develop a comprehensive program related to the specific DSWQ challenge. Some chapters include an intermediate, or "moderate," rating that is clearly defined within that chapter.