Finding out whether your stormwater and wastewater drains are accidentally connected is something every NZ homeowner should check — especially in older properties. Cross-connections are illegal under the NZ Building Code and can cause serious environmental harm, council fines, and unpleasant sewage overflows. The good news is there are some straightforward tests you can do yourself before calling in a licensed drainlayer.
Why Cross-Connections Are a Problem
In New Zealand, stormwater (rainwater from roofs, driveways, and paved areas) and wastewater (from toilets, sinks, showers, and appliances) must be kept in completely separate drainage systems. This is required under NZ Building Code clauses E1 (surface water) and G13 (foul water). When the two systems are accidentally joined — known as a cross-connection — raw sewage can discharge into stormwater drains and waterways, or stormwater can overload the wastewater network during heavy rain.
Cross-connections are particularly common in homes built before the 1970s, or where DIY drainage work has been done without proper oversight.
Visual Inspection First
Before running any tests, do a basic visual check:
- Locate your inspection chambers (also called manholes or rodding eyes) around the property. Lift the lids and note where each pipe leads.
- Check your downpipes. Trace each roof downpipe to see where it discharges — it should go to a stormwater drain or soakage system, not to a gully trap connected to the wastewater line.
- Look at gully traps. These are the small open-topped pots at ground level outside your home. Wastewater from laundries, baths, and sinks should discharge into gully traps. Downpipes should not.
- Check for obvious DIY connections — pipes that look like they've been joined together informally.
If anything looks suspicious, note it down before moving to the tests below.
The Dye Test (Stormwater Side)
This is the most common DIY method to check if stormwater is entering the wastewater system.
- Purchase drain tracing dye (available at plumbing suppliers or some hardware stores — look for a brightly coloured, non-toxic dye).
- Pour the dye into a stormwater inlet such as a downpipe or a surface drain on your property.
- Wait a few minutes, then check your wastewater inspection chamber or gully traps to see if the coloured water appears.
- If the dye shows up in the wastewater side, you have a cross-connection.
Tip: Do this test during dry weather so you're not confused by rainwater already in the system.
The Running Water Test (Wastewater Side)
This test checks whether wastewater is leaking into your stormwater drains.
- Locate your stormwater inspection chamber — the one that collects roof and surface water.
- Have a helper run water inside the house: flush the toilet, run the shower, and turn on taps simultaneously.
- Watch the stormwater chamber. If water levels rise or you see flow during dry weather, wastewater may be entering the stormwater line.
This test works best on a dry day when there's no rainfall to confuse the results.
The Smoke Test (Best Left to Professionals)
A smoke test is a more thorough method where a licensed drainlayer pumps non-toxic smoke into the drainage system and watches where it emerges. This can reveal hidden cross-connections, cracked pipes, and illegal connections that simpler tests miss. While the concept is straightforward, the equipment and expertise required mean this is best carried out by a professional.
CCTV Drain Camera Inspection
If you suspect a problem but can't pinpoint it, a CCTV drain camera inspection is the gold standard. A licensed drainlayer feeds a camera through your pipes to visually identify cross-connections, root intrusion, collapsed pipes, or illegal junctions. Many drainlayers across NZ offer this service, and it removes all guesswork.
What the Rules Say
Under the NZ Building Code and most territorial authority bylaws, it is illegal to connect stormwater to the wastewater network or vice versa. If your council discovers a cross-connection on your property, you may be required to fix it at your own cost — and fines can apply. Some councils actively audit properties, particularly during or after heavy rainfall events.
For more on drainage standards, BRANZ provides technical guidance relevant to NZ residential construction.
When to Call a Professional
Drainage work in New Zealand is restricted work under the Plumbers, Gasfitters, and Drainlayers Act 2006. Any physical work to alter, repair, or disconnect drainage connections must be carried out by — or under the supervision of — a licensed drainlayer registered with the Plumbers, Gasfitters and Drainlayers Board (PGDB).
You should call a licensed drainlayer if:
- Your DIY tests suggest a cross-connection exists
- You're unsure how to interpret your results
- You want a CCTV inspection or smoke test carried out properly
- You need any pipes altered, rerouted, or reconnected
- Your council has issued a notice requiring remediation
A qualified local drainlayer can be found through tradedirectory.co.nz.
Safety Note
Never enter a drainage inspection chamber or confined space yourself. Sewer gases including hydrogen sulphide can be lethal. If you need to inspect inside a chamber, keep your face clear and never lean in. Leave any confined-space work entirely to trained professionals. For more on confined space safety, refer to WorkSafe NZ.