To control discharge of municipal sewage waste and to channel the flow of ground water, sewer systems were created. Sanitary sewers collect household and commercial waste from toilets, showers and sinks. The sewage is then transported via sanitary sewer to a waste treatment facility. Storm sewers collect excess ground runoff and transport it to a water supply, i.e. a river or lake.

As long as there have been sewer systems, there have been leaks in a system. A leak in a sanitary sewer has several undesirable effects. It can collect groundwater, unnecessarily taxing the waste treatment facility. It can also release noxious or explosive sewage gases into the atmosphere. Groundwater containing pesticides or fertilizers can be hazardous to a sanitary water supply.

A small leak can grow and cause additional damage, even the collapse of a sewer line. To prevent leaks from causing damage to the system, municipalities must be vigilant in inspecting their systems.

Several techniques are used to identify leaks in a sewer system, such as adding dyes to the water or video camera inspection. Another proven technique is the sewer smoke test. In this test, a technician will blow smoke through a manhole or other opening with the aid of a fan. The smoke will follow a path of least resistance and will flow through cracks or other openings. Used in combination with a camera, inspectors can identify where the smoke flows through a crack or seam.

Those utilizing a smoke test look for several features in the product they use for testing. First, they seek smoke materials that are non-toxic. Second, they tend to choose products that do not leave a residue. The residue can become absorbed into sewage and be carried to the treatment facility. If toxic, it can affect treated water. Third, they tend to choose low odor chemicals for smoke production. Noxious odors can leech back into homes or businesses through the system. Modern technicians tend to avoid zinc oxide products in modern testing. Zinc Oxide can be considered a hazardous chemical and in sufficient quantities, can be harmful to a water supply.