Unfortunately, a standard garden hose doesn't have nearly enough pressure or mechanical action to flush established tree roots out of a drain. Roots that have infiltrated a pipe need to be cut, jetted at high pressure, or chemically treated — and in many cases, the pipe itself may need repair or replacement. Here's what you need to know before you reach for the hose.
Why Tree Roots Get Into Drains
Tree roots are naturally drawn to the warmth and moisture inside drain pipes. They typically enter through joint gaps, hairline cracks, or deteriorated rubber seals — especially common in older clay or concrete pipes. Once inside, roots grow rapidly and can cause partial or complete blockages, and over time they can crack or collapse the pipe entirely.
Common warning signs include:
- Slow-draining sinks, toilets, or floor wastes
- Gurgling sounds from drains
- Sewage smells in the yard
- Patches of unusually lush, green grass over the drain line
- Recurring blockages in the same location
What a Garden Hose Can (and Can't) Do
A standard garden hose delivers water at roughly 200–400 kPa — nowhere near enough to dislodge or cut through root masses. At best, a hose might shift a very minor, loose debris blockage, but it will not remove roots.
What can help with roots includes:
- High-pressure water jetting (hydro-jetting): Specialist drain-jetting machines operate at 3,000–5,000 kPa or more, using rotating nozzles that cut through root masses and flush debris away. This is the most common professional method.
- Mechanical drain augers (electric eels): A rotating cable with a cutting head physically cuts through roots. Hire units are available from some tool-hire shops, but they require skill to use safely without damaging the pipe.
- Root-killing chemicals: Copper sulphate or foaming herbicide products (such as those containing dichlobenil or metam sodium) can be flushed into the drain to kill roots over time. These are slow-acting and work best as a preventive measure after clearing, not as a first response. Always follow label directions carefully and check they are approved for drain use in New Zealand.
Can You DIY a Drain Root Blockage?
For above-ground or internal drain fittings (e.g., clearing a trap under a sink), a homeowner can generally do minor maintenance work. However, once you're dealing with underground drainage pipes, the situation changes significantly under New Zealand law.
Under the Plumbers, Gasfitters, and Drainlayers Act 2006, drainlaying work on sanitary drains is restricted work that must be carried out by — or under the supervision of — a licensed drainlayer. This includes cutting into, repairing, relining, or replacing underground drain pipes. Attempting this work unlicensed can result in fines and may void your home insurance.
A homeowner may generally:
- Use a plunger or hand auger on an internal fixture
- Pour approved root-treatment chemicals down a drain access point
- Flush a drain with a hose as a basic rinse (though this won't clear roots)
A homeowner must not (without a licence):
- Cut, repair, reline, or replace underground drain pipes
- Open or alter drain inspection chambers (in most cases)
- Connect new drain lines
If you're unsure where the boundary lies, contact the PGDB or your local council.
Getting a CCTV Drain Inspection First
Before spending money on jetting or chemicals, it's worth knowing exactly what you're dealing with. A licensed drainlayer can carry out a CCTV drain camera inspection to locate the blockage, assess root intrusion severity, and check whether the pipe is cracked or collapsed. This saves guesswork and helps you choose the right solution.
BRANZ research highlights that older NZ homes — particularly those built before the 1980s — are more likely to have clay or concrete pipes that are vulnerable to root intrusion and joint failure.
Longer-Term Solutions
If roots are a recurring problem, jetting alone is a temporary fix. Longer-term options include:
- Pipe relining: A resin liner is inserted and cured inside the existing pipe, sealing cracks and joints without full excavation. This is a popular, less-disruptive option.
- Pipe replacement: Where pipes are badly damaged, full replacement may be necessary. This requires a licensed drainlayer and, depending on the scope of work, may require a building consent — check with your local council, as some drain repairs fall under Schedule 1 exemptions. See MBIE Building Performance for guidance.
- Root barriers and tree management: Removing or relocating problem trees, or installing physical root barriers during landscaping, can prevent future issues.
When to Call a Professional
Call a licensed drainlayer if you notice any of the warning signs listed above, if a blockage keeps coming back, or if you suspect your underground pipes are cracked or root-damaged. Attempting to clear or repair underground drains yourself without a licence is illegal and can cause costly damage. You can find qualified local drainlayers on tradedirectory.co.nz.
Safety note: If you smell sewage gas (hydrogen sulphide) near a drain or inspection chamber, do not enter any confined space — this gas is toxic and potentially fatal. Contact a professional immediately and keep others away from the area. See WorkSafe NZ for confined space hazard information.