Water Vapor Testing
Seattle Public Utilities performs water vapor testing to locate leaks and pipe connection issues. This is a common practice where water vapor is sent through the sewer system so crews can visually track where it comes out through sewer vents, maintenance holes, and the ground.
What to Expect
- How you will be notified: You will receive a mailer a few weeks before testing and a door hanger 1-2 days before the inspection is expected to begin.
- No Utility Service Interruptions: Homes and businesses will continue to receive normal water and sewer services throughout the inspection period.
- Preparing Your Home: To prevent the water vapor from entering your home, residents are advised to run water for 30 seconds in all sinks, baths, and showers, and pour water into exposed floor drains 1-2 days prior to the testing. This ensures that drains are filled with water, which acts as a seal.
- Normal Observations: It is normal to see or smell the water vapor coming from maintenance holes in the street or right-of-way, sewer vents from roofs, or emerging from the ground. In such cases, no action is required.
- If Water Vapor Enters Your Home: If you detect or smell water vapor inside your house or building, open doors or windows to increase ventilation. The vapor should clear within a few minutes.
- Persistent Water Vapor Inside: If water vapor continues to enter your building, even after you pour water down the drains, please consider contacting a licensed plumber to investigate potential plumbing issues. You may also notify on‑site field representatives or contact SPU’s Operations Response Center (ORC) at (206) 386‑1800 for assistance.
You can learn more about Drainage and Wastewater by visiting the Shape Our Water website or the Side Sewers page.
This is a first step in gathering additional information about the sewer system layout. Once data is collected, SPU teams will use the information to develop workable neighborhood solutions for sewer overflows.
Trained SPU staff or contractors working on behalf of SPU. All crews carry identification and work vehicles will be marked. Crews will be working on the streets in front of homes and businesses.
Do not be alarmed! The water vapor may look like smoke, but it is a safe, non-toxic, non-staining water-based vapor.
Vapor from sewer vent stacks located on the roof is normal. Vapor from the yard, foundation, gutters, or downspouts may indicate improper or damaged sewer connections. Crews will document these findings, and SPU will follow up if needed.
Testing is quick. Most locations are tested for a few minutes at a time. Crews typically move through a neighborhood over several hours.
To prevent the water vapor from entering your home, residents are advised to run water for 30 seconds in all sinks, baths, and showers, and pour water into exposed floor drains 1-2 days before testing begins.
This ensures that drains are filled with water, which acts as a seal to prevent vapor from traveling through the drain into a house.
No. Testing occurs in the public sewer system. You will not need to be home during testing, and no one will be entering your property.
Yes. The water vapor is non-toxic, non-staining, and may have a mild odor.
The vapor does not activate standard smoke detectors or fire sprinklers. If you have a specialized fire detection system, contact SPU using the phone number on your door hanger or notice.
You may notice vapor coming in through your sink or the roof. Most homes and buildings will not experience vapor indoors. If you detect or smell water vapor inside your house or building, open doors or windows to increase ventilation. Any odor or visible vapor should only last a few minutes.
If water vapor continues to enter your building, even after you pour water down the drains, please consider contacting a licensed plumber to investigate potential plumbing issues. You may also notify on-site field representatives or contact SPU’s Operations Response Center (ORC) at (206) 386-1800 for assistance.
Crews and field representatives will be onsite in the unlikely event that any issues may arise. You may also contact SPU’s emergency Operations Response Center (ORC) at (206) 386-1800.
Yes, the industry has used the term “smoke testing”. SPU uses “Water Vapor Testing” as it is a more accurate description.