The residue from sewer backups contains bacteria that are dangerous to human health. Surfaces and objects contaminated by such sewer backups or ground water should be thoroughly cleaned and treated with an appropriate germicide before returning them to use. Unlike many other types of damage sewer backups are especially troublesome because the areas you don't see can be just as important as areas you do see. The pile of rugs and carpets as well as the padding provide breeding places that may not be reached by surface applications of a germicide. Hidden recesses within walls and floors should be opened for drying and direct germicidal contact with all surfaces. Some highly absorbent materials such as drywall, insulation, or cardboard cartons, may be more economical to replace than restore after exposure to sewage or ground water. The degree of exposure and the nature of the surfaces themselves will determine the precise actions required.
Since objects can look "clean" while retaining harmful bacteria it is important that germicidal treatments be applied in a thorough and methodical way so that all areas are treated, It is important to allow adequate time between treatments and rinse for the germicide to take full effect. Repeated treatments are sometime required.
When children or pets are present, it is sometime advisable to test after treatment to be certain that floor surfaces and furnishings have been restored to a wholesome condition. This can be accomplished by taking swab samples from affected areas and incubating them in a culture medium to measure the bacterial activity present in affected areas. Local health departments sometimes provide this service to citizens.