Smoke testing is a field investigation technique used in stormwater and sanitary sewer systems to identify leaks, illicit connections, and structural defects by introducing a non-toxic, artificially generated smoke into a closed drainage system and observing where the smoke escapes.
In practice, a blower is connected to a manhole or catch basin and forces dense, visible smoke through the underground piping network. Because the system is intended to be sealed except for designed inlets and vents, any smoke that emerges at unexpected locations indicates a potential issue. Investigators observe and document points where smoke exits, such as yard drains, roof downspouts, building foundations, cracks in pavement, or directly from the ground surface.
Smoke testing is particularly effective for detecting illicit connections, such as roof leaders, foundation drains, or sanitary sewer lines that are improperly connected to a stormwater system. It can also reveal defects like broken pipes, deteriorated joints, uncapped laterals, or holes in infrastructure that allow stormwater inflow or groundwater infiltration. In sanitary sewer systems, it is often used to locate sources of inflow and infiltration that contribute to system overloading and potential overflows.
The smoke used is specially formulated to be non-toxic, non-staining, and safe for humans, animals, and vegetation when used as directed. It is typically white or gray and has a noticeable but harmless odor to make its presence obvious. Because the smoke travels along the same pathways as air or gases within the system, it is an effective surrogate for identifying pathways that water or pollutants may follow under certain conditions.
Unlike dye testing, which traces liquid flow, smoke testing primarily identifies openings and connections that allow air exchange. As a result, the two methods are often used together to provide a more complete understanding of system behavior, with smoke testing locating physical defects and dye testing confirming hydraulic connectivity.
Smoke testing is a rapid, cost-effective, and widely used method for diagnosing drainage system integrity, supporting maintenance planning, and ensuring compliance with stormwater management regulations.