Yes, unblocking an outside stormwater drain is generally a job a homeowner can tackle safely, provided the blockage is straightforward and you take a few sensible precautions. Stormwater drains carry rainwater runoff away from your property, and keeping them clear is important — especially in New Zealand's wet winters. Here's what you need to know before you grab a pair of gloves and get started.
Understanding Your Stormwater System
Before you start, it helps to know what you're dealing with. Stormwater drains collect rainwater from roofs, driveways, and paved areas and channel it to the street, a soakpit, or a waterway. They are separate from your wastewater (sewage) system, which carries water from toilets, sinks, and showers.
Confusing the two is a common mistake. If you notice foul smells coming from the drain, or if sewage is backing up, stop immediately — that's a different (and more serious) problem that may require a licensed drainlayer. Check with the Plumbers Gasfitters & Drainlayers Board if you're unsure about what work is restricted.
Common Causes of Stormwater Blockages
Most outside stormwater blockages are caused by:
- Leaf litter and debris accumulating in grates and sumps
- Silt and mud washing in over time
- Tree roots infiltrating older clay or concrete pipes
- Collapsed or offset pipes (less common, but serious)
- Rubbish accidentally washed in
The good news is that the first two causes are very DIY-friendly.
What You'll Need
- Rubber gloves (heavy-duty, elbow-length if possible)
- Safety glasses
- A drain rod set or a garden hose with a jet nozzle
- A trowel or scoop for removing debris
- A bucket for waste
- Old clothes you don't mind getting dirty
Drain rod sets are available from Bunnings or Mitre 10 and are a worthwhile investment if you have mature trees near your drains.
Step-by-Step: How to Unblock a Stormwater Drain
1. Safety First
Always wear gloves and eye protection. Stormwater can carry bacteria, animal waste, and other contaminants. Wash your hands thoroughly afterwards. Never work near a drain during heavy rain or if there is any risk of a sudden surge of water.
2. Remove the Grate or Cover
Most stormwater grates simply lift off or are held by a couple of screws. Use a flat-head screwdriver if needed. Set the grate aside and clean it separately.
3. Clear Surface Debris
Scoop out any leaves, silt, and rubbish from the sump (the pit beneath the grate) by hand or with a trowel. Place waste in a bucket — don't hose it back into the drain or onto a neighbour's property.
4. Check the Flow
Pour a bucket of water into the sump. If it drains away freely, the blockage was just surface debris — job done. If it pools, the blockage is further down the pipe.
5. Use Drain Rods
Feed drain rods into the outlet pipe, turning them clockwise as you push (never anti-clockwise, or the rods may unscrew underground). Work the rods back and forth to break up the blockage. Flush with a garden hose as you go.
6. Flush and Test
Once water flows freely, flush the system thoroughly with a hose. Replace the grate securely.
What You Should NOT Put Down a Stormwater Drain
Under the NZ Building Code and most council bylaws, stormwater drains must only carry clean rainwater runoff. Never dispose of:
- Chemicals, paint, or solvents
- Concrete washwater
- Wastewater or sewage
- Cooking oils or food waste
Disposing of contaminants into stormwater drains can result in significant fines from your local council and cause environmental harm.
Maintenance Tips to Prevent Future Blockages
| Task | Frequency |
|---|---|
| Clear leaves from grates | Monthly (autumn/winter) |
| Flush drains with a hose | Every 3–6 months |
| Check for root intrusion | Every 2–3 years |
| CCTV inspection (professional) | Every 5+ years for older pipes |
Regular maintenance is the best way to avoid costly blockages. BRANZ has useful guidance on maintaining drainage around your home.
When to Call a Professional
Some situations are beyond a DIY fix. Call a qualified drain cleaner or licensed drainlayer if:
- Water won't clear after rodding and flushing — the blockage may be deep or the pipe may be collapsed
- Tree roots are suspected (a professional will use a high-pressure water jetter or CCTV camera to assess)
- Sewage smell is present — this may indicate a cross-connection or a broken wastewater pipe, which is restricted work under the Plumbers, Gasfitters, and Drainlayers Act 2006
- Flooding is recurring despite clearing the drain — your system may be undersized or damaged
- You're unsure whether the drain connects to the council network — any work on a public drain requires council approval
For complex drainage work or any work that involves connecting to or modifying the drainage system, you'll need a licensed drainlayer. You can find qualified local drain cleaners and drainlayers on tradedirectory.co.nz.
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