This chapter discusses the drinking water practitioner’s most important function: ensuring that water delivered to the public is properly treated and arrives as the clean, wholesome, safe product that it must be. Moreover, it also covers the innovative approach taken by the Hampton Roads Sanitation District to replacing one-and-done usage with one-and-redone usage. The chapter provides a brief overview of each of these unit processes, which constitute a typical drinking water treatment system for surface water supplies, in addition to a brief discussion of alternative approaches. Large surface water treatment plants may employ a variety of screening devices, such as trash screens (or trash rake), traveling water screens, drum screens, bar screens, or passive intake screens. Primarily used in wastewater treatment applications, bar screens are also employed in some water treatment facilities. A bar screen consists of straight steel bars welded at both ends to horizontal steel members and is automatically cleaned by one or more power operated rakes.