AWWA's most popular handbook for distribution operator personnel is an indispensable reference for operators and supervisors alike on water distribution system operation and equipment. This fourth edition is based on the operator certification knowledge requirements included in the Associated Boards of Certification (ABC) Need-To-Know criteria, as well as that of several state certification boards (e.g. California, Pennsylvania, and Texas). Several new chapters cover topics that have emerged since the publication of the last edition, and others, including the regulatory overview chapter, were revised extensively. New chapters describe the management approach to distribution system operation and the operational practices operators can use to improve system performance. The disinfection of pipelines and storage facilities is now included as its own chapter. And the math calculations that distribution system operators need to know are included as concrete examples of what operators need to know.