Smoke testing is used to locate specific defects (leaks) in sewer mains and laterals that contribute infiltration and inflow to the sewer system. Smoke testing involves injecting a non-toxic vapor (smoke) into the manholes and following its path of travel in the mains and laterals. Coloured dye is added to the storm drain water. Dyed water appearing in the sanitary sewer system indicates an existing connection between the sewer and storm drain system. Also, coloured dye can added to the sewer connection through an on-site fixture (toilet, sink, etc.) to help determine the approximate connection point to the City sewer system.