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Melbourne’s Sewerage Systems

Why sewerage systems are important

Melbourne enjoys a world class sewerage system that is central to preserving the health of our community and the health of our environment. Melbourne’s sewerage system safely collects and transfers sewage to treatment facilities without risking community health or adversely affecting the environment. Water authorities operate and maintain reliable sewerage systems with sufficient capacity to safely collect and transfer sewage.

Melbourne Water sewer spills

The video below demonstrates how Melbourne’s world-class sewerage system works and what initiatives are being introduced to make it even better. It also provides a number of tips on how you can assist with the efficiency of your local sewerage network.

View the transcript

Extreme stormwater events

Sewerage systems are generally built with significant capacity to contain peaks in daily flows through to inflows from significant rainfall events, and as a result, sewage spills rarely occur.

In Australia, stormwater and sewerage and stormwater operate separately, but during periods of heavy rain, stormwater can still enter the sewerage network, including even relatively new systems via:

  • Maintenance holes (for access)
  • Property surface fittings such as gully traps and air vents
  • Groundwater infiltration
  • Broken or badly connected sewer service line; and
  • The cross connection of stormwater downpipes to the sewerage pipes within properties.

When sewerage systems are designed, an allowance is made for stormwater ingress. In Melbourne, the performance objective is set by the Environment Protection Authority (EPA) which compels sewers to be designed with the capacity to contain flows emanating from a 1 in 5 year storm event. Typically this storm event is equivalent to 25mm of rain occurring in 1 hour.

Despite this, during extreme storm events (beyond a 1 in 5 year event), stormwater may still exceed the system’s capacity, resulting in diluted sewage being discharged at the designed overflow points (via Emergency Relief Structures) ERS allow controlled spilling at points in the system where the local environment can cope with the additional flow and prevent spilling at more sensitive locations.

Although these types of sewage spills rarely occur, in recent times Melbourne has been experiencing rainfall events of increasing intensity and at a greater frequency than in the past. Significant investment has been made to increase the capacity of the system and minimise these types of spills.

Heavy rains also wash other pollutants such as dog droppings, oil, nutrients and litter into Melbourne’s rivers and creeks which can undermine water quality. As a precaution waterway users should avoid contact with rivers and creeks for 48 hours after heavy rains.

Sewer Blockages

Occasionally blockages occur in the sewerage system due to tree root penetration of the pipes, build-up of fats, oils and grease, or from pipe breaks and collapses. We undertake field assessments using robot cameras to monitor the condition of the sewers to identify sewer cleaning works as well as pipe renewal works. In high risk areas the sewerage system is fitted with monitoring devices that alert our operators to any potential issues in the network, and preventative actions can be undertaken before a spill occurs.

In dry weather, sewer blockages are the main reason for sewage spills. The most common causes of sewer blockages include:

  • Tree roots penetrating the pipe.
  • A build-up of oils and fats.
  • Household waste such as sanitary products and food scraps that have been flushed or put down the sink.
  • Damaged and broken pipes allowing soil and pieces of the pipe to block the sewer.

Sewer spills from blockages are generally smaller in volume and are contained within a defined area which allows for easy clean-up of the spill site. Water authorities implement programs that improve the system’s reliability and reduce the risk of sewer blockages.

What you can do?

Everything that goes down the kitchen, laundry and bathroom sink or that's flushed down the toilet ends up in the sewerage system. Putting the wrong things down the sewer affects our ability to treat and reuse the water and can cause damage to the sewerage system.

  • Use a sink strainer to prevent food scraps and other household waste from going down the drain. Consider using a compost heap or worm farm to recycle food scraps for your garden.
  • Pour kitchen fats and oils into a container, seal it, and throw it in the bin.
  • Wipe greasy pots and pans with a paper towel before washing.
  • Dispose of items such as cotton buds, nappies, condoms, sanitary products and their wrappers in the household rubbish.
  • Use less detergent. The average household uses three times more detergent than manufacturers recommend.
  • Choose a washing detergent with a low salt content. Concentrated detergents often contain much less salt than conventional varieties.
  • Ask your local pharmacy or council for advice on how to dispose of medicines and hazardous chemicals.
  • When next renovating your home, ask your plumber to check that your stormwater plumbing is not connected to the sewer.

For further information contact:

City West Water

Melbourne Water

South East Water

Yarra Valley Water

Program Partners

Department of Environment and Primary Industries Environmental Protection Agency Melbourne Water