What causes wet weather overflows?

Storm image Wet weather overflows can occur when rainwater overwhelms the stormwater network and spills over into the sewer system. They tend to happen during significant rainfall events, with properties in low-lying and flood-affected areas most at risk. They can also occur as a result of improper stormwater-to-sewer connections.

Stormwater and sewerage networks are separate systems, designed differently to meet different needs. 

  • Stormwater pipes collect rainwater run-off and direct it into the stormwater network where it’s fed into waterways.
  • The sewerage network carries sewage from bathrooms, kitchens and laundries to treatment plants for processing.
  • While sewer pipes are typically designed to carry five times the average dry weather flows, they are generally much much smaller in diameter than stormwater pipes. If rainwater overwhelms the stormwater network and spills over into the sewer system, sewage may back up which can lead to an overflow.

The local council manages and maintains the stormwater network, which directs untreated stormwater to local creeks, rivers and waterways. Urban Utilities’ sewer pipes collect wastewater and sewage from your property, transporting it to a treatment plant.

Frequently asked questions


If your property has been flooded by the sewer as a result of wet weather, please call us immediately on 13 23 64 (24/7).

If there has been an outdoor wet weather overflow and you would like us to attend to clean up, you can report this online at urbanutilities.com.au/fault 

If a wet weather overflow occurs, we will send a crew to assist and clean up the area as soon as we can. Please be aware there can be a delay while we wait for heavy rain to subside and the overflow to stop before our crews can commence clean-up activities.

Read more about steps you can take if your property has been damaged by a wet weather overflow.

A Queensland Urban Utilities worker

We have a range of programs to help reduce wet weather overflows by:

  • Prioritising network upgrades in low-lying areas where wet weather overflows occur most often.
  • Providing ongoing maintenance, including CCTV inspections and regular cleaning, to identify cracks and clear blocked sewer pipes.
  • Utilising innovative technologies and remote controlled robots to access and inspect the sewer system.
  • Conducting smoke testing to find where stormwater is entering the sewerage system and contributing to overflows.

Homeowners must take reasonable steps to ensure their plumbing and drainage is kept in good condition and operates correctly. Some things you can do:

  • Prevent stormwater from flooding your overflow relief gully (ORG). This is a grated outlet located in the ground outside your home, usually near the laundry, which acts as a release valve and helps prevent sewage from flooding your house by directing the overflow outside
  • Your ORG should be installed at least 75mm above ground level to avoid collecting stormwater.
  • If your ORG is low-lying or floods easily, an ORG cap can be fitted to help prevent inflows.
  • Check stormwater pipes from your roof, driveway or patio are not connected to the sewerage network or your ORG. Improper connections can contribute to overflows.
  • Keep reflux valves (if installed) and all other plumbing and drainage in good condition through regular maintenance by a licensed plumber.
  • Look after household pipes to prevent blockages. Only flush human waste and toilet paper down the toilet and use a sink strainer in the kitchen.
  • Think before planting trees and shrubs as they damage pipes and can cause blockages, which also lead to overflows.
  • Prepare for severe weather during storm season.