Charles County, Maryland

Sanitary Sewer Smoke Testing

Sanitary Sewer Smoke Testing

Edward Gorham
Chief of Technical Support

The Charles County, MD, Department of Public Works - Utilities uses smoke testing to find cracks, breaks, and other problems with sewer lines that need to be repaired or possibly replaced. If you would like to see a video that demonstrates what smoke testing is and how it is used, please click on the link below.  Clicking on the link will take you to the YouTube© website, which is outside the CharlesCountyMD.gov website.  If you do not want to visit the YouTube© website, please do not click on the link.

Please note that although this video was created by and for the Charleston Water System, it provides a good overview of how smoke testing works in Charles County as well.  

The smoke is safe and non-toxic to humans and pets, but customers with respiratory issues should notify the Department at 301-609-7400 before smoke testing is to occur in your neighborhood.

Smoke Testing Link Graphic

Click here for the Smoke Testing Video.

Sanitary Sewer Smoke Testing FAQs

What is the purpose of smoke testing?
Public Notification (How will I be notified?)
How does smoke testing work?
What are the benefits of smoke testing?
Is the smoke harmful?
Will smoke testing of the sewers allow smoke to get into my home?
What does it mean if smoke enters my house?
How may the smoke enter my house?
What should I do if smoke gets into my house?
How long will the testing take?
What should I do to prepare for smoke teting?
Do I have to be home during testing?


What is the purpose of smoke testing?

The purpose of smoke testing is to find potential points of inflow and infiltration in the public and private portions of the sanitary sewer system that could lead to high flows during storm events.  Smoke testing can also help locate the following:

  • Buildings that have downspouts, cellar, yard or basement drains
  • Catch basins and parking lot drains
  • Any connections between sanitary sewers and storm drains
  • Defective sewer connections that could allow sewer gases into a building (return to top)

Public Notification

Field crews will distribute a notice door to door approximately 24 to 48 hours in advance. Police, Fire and the Public Works Official will also be notified daily of work area. (return to top)

How does smoke testing work?

During smoke testing, field crews blow air and smoke into the sanitary sewer system in the street and monitor where smoke escapes the system. The smoke, under pressure, will fill the main line as well as any connections and then follow a path of any leak to the ground surface, quickly revealing the source of the problem. Only enough force to overcome atmospheric pressure is required, and smoke should escape from building roof vents. (return to top)

What are the benefits of smoke testing?

Smoke testing is the most efficient and cost effective way to locate and identify where unauthorized water is entering the public and private portion of the sewer system. The smoke is harmless and will disappear after only a few minutes. The testing is also a cost-effective way to find areas of the sewer system that need improvement. Smoke testing will also help identify plumbing leaks in buildings. Sewer gases can cause health problems for building occupants. (return to top)

Is the smoke harmful?

NO.  The "smoke" is not true smoke. It will not harm your health or leave a stain and will disappear rapidly without leaving an odor. If the smoke enters your home, it may make you cough, but the smoke is:

  • Non-toxic
  • Non-staining and odorless
  • Harmless to humans, pets, plants, food and material goods
  • Creates no fire hazard (return to top)

Will smoke testing of the sewers allow smoke to get into my home?

No, provided that your plumbing is installed and functioning properly, and provided "traps" are filled with water. Drains that are used frequently should be okay. If you are not sure, simply run water down the drain for a minute to ensure that the trap is not dry. It is important to locate dry traps as they could allow sewer gases to enter the home. Dry traps are most commonly found in basement floor drains that are used only during rare flood events or in unused fixtures. Please thoroughly check your home. (return to top)

What does it mean if smoke enters my home?

If smoke enters your home during the test, it may indicate there are deficiencies in the plumbing that may allow potentially dangerous sewer gases to enter. (return to top)

How may the smoke enter my house?

Since plumbing fixtures in your home or business are connected to the sanitary sewer system, there is the potential for the smoke to enter if the drains are not connected properly. This happens particularly under the following circumstances:

  • The vents connected to your building's sewer pipes are inadequate, defective or improperly installed
  • The traps under sinks, tubs, basins, showers and other drains are dry, defective or improperly installed
  • The pipes, connections or seals in the wastewater drain system in and/or under your building are damaged, defective, have plugs missing or improperly installed. (return to top)

What should I do if smoke gets into the house?

  • Do Not Become Alarmed
  • Open windows to allow ventilation and note the location of the smoke emission; smoke will clear within a few minutes
  • Exit the building and notify smoke testing personnel in the area. (return to top)

How long will the testing take?

While crews might be in your area for a few hours, each actual smoke test setup takes approximately 15 minutes to complete. Most houses will only be within the testing area for one or two tests. (return to top)

What should I do to prepare for smoke testing?

When you receive notice that smoke testing will take place, you should:

  • Check to see that all drain traps under basins, washing facilities and floor drains contain water; simply flush toilets and run or pour water into all drains, including unused fixtures and floor drains.
  • If there is an individual in your home or business who has respiratory problems and/or mobility limitations, or if you have any additional questions, contact the Charles County Department of Public Works - Utilities at 301-609-7400. (return to top)

Do I have to be home during testing?

No.  Inspection crews will not need to enter your home unless smoke is present and you want them to help identify the defect. You are not required to allow entry to our crews. (return to top)