In this chapter, we discuss the basics of wastewater collection systems. In Volume II of this handbook series, as you might expect, wastewater collection and conveyance systems are discussed in greater detail. Wastewater collection systems collect and convey used or spent water (wastewater) to the treatment plant. Wastewater collected from homes, businesses, and industries and conveyed to a wastewater treatment plant comprise a sanitary sewer system. A similar system known as a stormwater collection system conveys water resulting from the runoff of rain and snow from buildings and paved and unpaved areas to a natural watercourse or body of water, usually without treatment. This type of system is also known as a storm sewer. In the past, some sanitary sewers and storm sewers were combined into one system; however, during heavy rain events the wastewater treatment plants served by combined sewers often became hydraulically overloaded and washed out into the receiving stream, causing complete treatment system failure. For this reason, combined sewers are now uncommon. The complexity of the system depends on the size of the community and the type of system selected. Methods of collection and conveyance of wastewater include gravity systems, force main systems, vacuum systems, and combinations of all three types of systems.