Blocked drains and tree roots on the Sunshine Coast
Tree roots are the single largest known cause of sewer blockages in Unitywater’s network, and Buderim tops the list for root blockages. Here’s how to spot the signs early, work out whose pipe it is, and stop it happening again.
Written by Cassel’s Plumbing & Gas, Bli Bli. Facts checked against the official sources listed at the end. Updated 11 October 2026.
What Unitywater’s figures show
3,043 blockagesAttended by Unitywater crews across Moreton Bay, the Sunshine Coast and Noosa in 2024–25.
614 from tree rootsAbout one in five blockages, making roots the single largest known cause.
Buderim firstBuderim, Clontarf and Caboolture had the most tree root blockages.
The other causesFats, oils and grease, and foreign objects that were flushed or poured down sinks.
Source: Unitywater media release, 17 November 2025.
Why roots get into sewer pipes
Roots go looking for water, and a sewer pipe is a steady supply. Fine root tendrils get into cracked pipes and joints, then thicken and spread inside, catching toilet paper and waste until the line blocks. Older pipes with more joints and cracks are the most vulnerable, and established suburbs with mature trees and gardens, like much of Buderim, give roots plenty of opportunity.
Clearing the roots restores flow, but roots that have found a way in tend to come back. Repeat blockages on the same line usually mean the damaged section needs repairing or replacing.
Signs of a blocked drain
Sinks, showers and baths draining slowly, often several at once
Gurgling from plug holes or the toilet when water runs elsewhere in the house
The toilet bowl rising when flushed, then draining slowly
Sewage smells inside or in the yard
Water or sewage coming up through the overflow relief gully outside
Wet, sunken or unusually green patches along the line of the sewer pipe
When several fixtures play up at once, the blockage is usually in the main line rather than in one fixture’s pipe.
Your pipe or Unitywater’s?
Your pipes: Unitywater says property owners are responsible for all the pipework and plumbing fixtures on their private property.
Unitywater’s pipes: pipes on public land and on Unitywater’s side of the property boundary are Unitywater’s responsibility.
If you’re not sure where the blockage is, Unitywater’s advice is to call a licensed plumber. If the plumber finds the blockage is in Unitywater’s pipe, they stop work and report it, and Unitywater sends a crew. If the problem is clearly on public land or on Unitywater’s side of the boundary, call Unitywater directly on 1300 086 489.
The overflow relief gully
The overflow relief gully (ORG) is the grated outlet in the ground outside, usually near the kitchen, laundry or bathroom. If the sewer backs up, it’s there to let sewage overflow outside rather than up through your toilets and shower drains. Unitywater notes that overflows happen on private land through ORGs, or inside homes through toilets and shower drains.
Keep the grate loose-fitting, uncovered and clear. Don’t pave, tile or build a garden bed over it.
It should sit slightly above the surrounding ground so rain and garden water can’t run in.
If it’s overflowing, stop using water in the house and call a plumber.
What to do when a drain backs up
Stop using water: toilets, showers, the washing machine and the dishwasher.
Keep children and pets away from any sewage, and wash your hands after any contact.
Don’t pour chemical drain cleaners into a sewer blockage. They rarely shift roots and make the job more hazardous for whoever clears it.
Call a licensed plumber. Sewage coming up inside the house is an emergency: see emergency plumbing.
What not to flush or pour down the sink
Unitywater’s list of the things that cause blockages:
Wet wipes, including ones labelled flushable
Sanitary products, cotton buds, condoms and medications
Cooking oils and fats: collect them in a container and put them in the bin
Food scraps: scrape plates into the bin or compost, and use sink strainers
Preventing root blockages
Plant at least 1.5 m from pipes, as Unitywater recommends, and choose species carefully. Keep large, thirsty trees well away from the sewer line.
Know where your pipes run. Unitywater has a free online mapping tool showing its infrastructure on your property, and it helps to know where your private sewer line runs before you plant or dig.
Keep downpipes on stormwater. Unitywater asks owners to check their downpipes connect to the stormwater system, not the sewer.
Fix the cause after a repeat blockage. If roots keep returning to the same spot, repairing the damaged pipe is the long-term fix rather than clearing it again and again.
If the roots are in pipes on your property, the property owner is responsible. If the blockage is in Unitywater’s pipe, on public land or on its side of the boundary, Unitywater is responsible for fixing it once it’s reported.
How far from the sewer should I plant a tree?
Unitywater recommends planting trees at least 1.5 m away from pipes and choosing species carefully. Larger, thirstier trees are better kept further away.
Why does Buderim have so many tree root blockages?
Unitywater’s 2024–25 figures had Buderim with the most tree root blockages in its network. It hasn’t published a reason, but established suburbs with mature trees and older pipes give roots more chances to get in.
What is the grate outside that overflows?
That is the overflow relief gully. It lets sewage overflow outside rather than inside the house when the sewer is blocked. If it overflows, stop using water and call a plumber.
