Which term best describes water that enters a sewer system unintentionally due to defects?

The term that best describes water entering a sewer system unintentionally due to defects is infiltration. Infiltration refers specifically to water that seeps into the sewer system through cracks, joint failures, or other imperfections in the sewer infrastructure. It typically occurs during dry weather and is often a slow, continuous process as groundwater penetrates the system.

In contrast, inflow is water that enters the sewer system during wet weather, usually from surface runoff or direct connections, such as downspouts and storm drains. Runoff refers to water that flows over land surfaces into water bodies or drainage systems, typically after rain events, and is not a result of defects in the sewer system itself. Leakage is a more general term that can refer to any kind of unintended escape or entry of fluids through defects, but it does not specifically denote the movement of water into the sewer system. Therefore, infiltration is the most precise term for describing the unintentional entry of water into sewers due to structural issues.