Inflow & Infiltration


Inflow and infiltration refers to water and stormwater that enters the sewer system.


Inflow is the direct discharge of stormwater to the sewer system, often from low lying gully traps, yard drains and roof downpipes and cross connections from stormwater drains that connect directly to the sewer.


Infiltration is the stormwater that seeps into the ground and enters the sewer system, including sewer service connections, through defects, cracks and joints in the pipes.


During periods of heavy rain, increased inflow and infiltration can overwhelm the sewer system and cause overflows. This reduces the network capacity, increases the cost associated with extra wastewater pumping and treatment and can lead to the contamination of private properties.

Council is continually maintaining the sewer system to minimise these overflows.

In order to manage the risks, property owners are required to ensure stormwater does not enter the sewer system. If this occurs on your property, you must contact a plumber straight away to have it rectified.

Problems common to private properties include:

  • Stormwater flowing into gully traps that are too low.
  • Downpipes from a roof connecting to sewer pipes or gully traps.
  • Drainage pipe joints leaking.
  • Cracked pipes.

Last updated: 10 Mar 2022