Smoke testing in our wastewater network

Smoke testing involves injecting a dense, non-toxic and odourless smoke into the drainage (sewer or stormwater) system at a manhole and watching to see where the smoke escapes. The smoke fills the main pipe and any connected pipes, and follows the path of any breaks in pipework to the ground surface.  

The purpose of smoke testing is to identify areas within the wastewater or stormwater network that need attention.  

Our stormwater network is designed to collect only rainwater runoff from roofs, roads and other hard surfaces.   

Our wastewater network is designed to collect wastewater from properties, not rainwater and other surface water.   

Smoke testing will help identify any places where the stormwater system is connecting to the wastewater network.   

When other water enters the wastewater network (especially in heavy rain), it mixes with the untreated wastewater and can overflow. Too much stormwater going through the wastewater treatment plant can also wash away the special bugs that treat our wastewater. This affects our treatment processes.

Smoke testing will help identify any stormwater connections to the wastewater network (cross-connection).  

Smoke testing is common practice around New Zealand.  

Before each new round of smoke testing, we notify the residents who may be affected. We do this by:  

• sending a letter to all houses in the area selected for testing  
• posting on Facebook groups.  

We also advise the fire service.  

No. The ‘smoke’ is not true smoke. It is a harmless white vapour – the same non-toxic substance used in smoke machines at concerts. It is considered safe for humans, animals and plants, leaves no residue or stains, is not a fire hazard and will disappear rapidly without leaving an odour. 

Since any vapour can be an irritant, direct contact with the smoke may cause minor respiratory irritation in some people.  

People with respiratory problems such as chronic asthma or emphysema should avoid direct exposure to the smoke. Please contact Council to discuss your situation further if you have concerns about upcoming smoke testing:  

Phone: 09 430 4200

Smoke appearing in your home may indicate that there is a problem with your plumbing. If you see smoke in your home during our testing, contact a licensed plumber to inspect and make any repairs needed.  

If your plumbing is installed and working properly, your U-traps will prevent smoke entering your home. A U-trap is a U-shaped section of your drainpipe that is always full of water. The water acts as a barrier, preventing sewer gases from getting into your home through sinks and drains. If there is no water in the trap, it will not work properly.

Dry traps are most often found in floor drains and bathroom drains that aren’t used often. We recommend running some water into infrequently used drains or fixtures prior to smoke testing. 

Do not be alarmed.  

Open windows to allow ventilation and note where the smoke is coming from; it will clear in a few minutes.  

Leave your home and notify the smoke-testing team in the area. They can confirm that the smoke is from our testing and is not caused by a fire.  

If smoke enters your home during the test, there may be problems with your plumbing. These problems could allow potentially dangerous sewer gas to enter. Please contact your plumber immediately.  

If you have any doubt as to the source of the smoke in your home or property and suspect a fire, please phone 111 and ask for "fire".

Ensure all drain U-traps contain water by running some water into all drains and fixtures before smoke testing. This is particularly important for floor drains and bathroom drains that aren’t often used.  

If there is an individual in your home or business with breathing problems and / or mobility limitations, or if you have any additional questions, please contact Council:

Phone: 09 430 4200

Yes, smoke alarms may be activated during smoke testing. If possible, open windows and / or doors for ventilation.

If you have any doubts about the origin of the smoke, phone 111 and ask for "fire".

We can’t do smoke testing when it’s rainy or very windy, so the weather can sometimes cause delays. However, we will let you know by mail when we plan to do smoke testing in your area.

If we are smoke testing the wastewater network, smoke will be seen coming from sewer vents (also known as terminal vents) on roofs of homes. This is normal and indicates that smoke has filled the sewers.

Smoke may also be seen coming from building foundations, manhole covers, or cleared sections with existing sewer connections.  

If we are smoke testing the stormwater network, smoke will be seen coming from roof guttering, road sumps and manhole covers.

No, the smoke is a vapour and cannot block the pipes.

Council will use the findings to help plan future infrastructure improvement projects and to identify changes required to stop stormwater and other surface water from getting into the sewer system or vice versa. Depending on the findings, we may also undertake immediate repairs to the sewer system.  

As there are drainage pipes located in your property, Council staff or representatives may require access to your property to check that smoke is exiting from the expected locations.

Council will not require access inside the building or house and you do not need to be home during the smoke testing.