Fluorescent dyes are commonly used in the detection of sewer leaks, according to Pollard Water. Fluorescent dyes differ from nonfluorescent dyes in that they absorb light at a certain wavelength and emit the light, rather than reflecting certain wavelengths as nonfluorescent dyes do. Where dyes are used to detect sewer leaks, simple tablets can be used for small sewer systems, while larger cone- and doughnut-shaped tablets are necessary to detect leaks in larger systems. Rather than simply dropping a tablet directly into a sewer system, servicers often dissolve the dye in a small amount of water to create a concentrated liquid dye that they then pour into the sewer system.
Fluorescent dyes are used in sewer systems because of the lack of available sunlight and artificial light within the pipes. To detect a fluorescent dye within the system, technicians use a black ultraviolet light to detect the dye within the water. Fluorescent dyes are available in red, blue and yellow/green colors. Nonfluorescent dyes are useful when sufficient light is available for the dye to be viewed in a sewer system.
Dye tests are used to test sewer lines in large municipal sewer systems and in the checking of septic systems and toilet leaks. Flood and emergency sewer systems can be checked for leaks, along with leak testing for storm drain systems. In toilet leak detection, a dye tablet goes in the tank, and the water in the bowl will change color where a leak exists. Other uses of dye tests include pollution testing of rivers, lakes and streams.
Alongside municipal utilities companies, the regular users of dye testing are commonly private water and sewer repair companies. Scientists and academics also use dye tests to complete studies of flow rate and flow mapping. Power plants use dye testing to complete tests of piping systems within the plant.