On-site Wastewater Management Systems (OWMS)

Properties without a sewer system connection will require an OWMS to treat and then recycle or dispose of wastewater within property boundaries.

An OWMS is commonly referred to as septic or a septic tank system.

OWMS have the potential for major environmental and human health risks, because of the pathogens and toxins they contain. Council has a commitment to administering and enforcing relevant OWMS legislation, and along with persons in control of an OWMS, a responsibility to minimise the impact of OWMS on public health and the environment.

Before you start installing or altering a septic system, follow these steps:

  1. If required, obtain a planning permit.
  2. Submit an application form to Install/Alter a Onsite Wastewater Management System and pay the applicable fee (alternatively your plumber or builder can assist with this)
  3. Obtain a permit to install (PTI) a Onsite Wastewater Management System.
  4. Install or alter the OWMS (Council must be notified 7 days prior to arrange a installation inspection)
  5. Council must conduct a final inspection to ensure all requirements are met.
  6. Council will issue you with a certificate to use (CTU) the system once approved. The system cannot be used until a CTU is issued. For new dwellings, a CTU must be issued before a Certificate of Occupancy can be issued by your Building Surveyor.


Applying to install or alter an OWMS

Prior to the installation or alteration of any OWMS, a permit must be obtained

  • For systems that can treat up to 5,000 litres a day, you can apply through Council.
  • For systems that can treat more than 5,000 litres a day, you need an operating licence and a development licence from the EPA. You don’t need further approval from Council.


When you submit an application to install or alter a septic system, ensure you have:

  • Site plan of proposed effluent field (ensure features such as waterways, dams and buildings are included)
  • Floorplan of all dwellings on site
  • Certificate of Conformance of proposed system
  • A Land Capability Assessment if requested during the planning process.


All OWMS works must comply with the permit issued by Colac Otway Shire, the Environment Protection Act 2017, the EPA Code of Practice for Onsite Wastewater Management and the relevant Australian/New Zealand Standards.

If your OWMS application is approved, the licensed plumber detailed on the permit must contact the Health Protection Unit to arrange an inspection of the system prior to backfilling. Seven days’ notice is preferred, prior to the commencement of works.   

System type and Disposal Method

There are a number of different types of OWMS available. To choose a system that is right for you and your property, you should liaise with Council's Health Protection Unit, your Land Capability Assessment provider and a licensed plumber to ensure that the system conforms to relevant Australian and New Zealand Standards and Council's Domestic Wastewater Management Plan.

When planning where to locate the septic system, you should consider:

  • Future use of the land – as it can’t be used in the future for other building etc.
  • Minimum distances to boundaries, watercourses (including dams), other buildings, swimming pools, tennis courts and driveways. These distances can be found in the Environment Protection Authority Code of Practice (891.4).
  • Where livestock is kept – as they can’t be kept on an effluent disposal area.
  • Distance to nearby trees and native vegetation.
  • Suitable plants and vegetation for the Effluent Field (see link at the bottom of this page)

Land Capability Assessment (LCA)

Whichever system you choose, you may be required to conduct a Land Capability Assessment (LCA). In unsewered areas, a LCA should be undertaken for each site that requires the installation of an OWMS, unless Council is satisfied the site is low risk or sufficient information (e.g. soil permeability rates, soil types, depths to water table, fractured rock and other limiting factors) has already been gathered about the site.

Some examples of when an LCA may be required to support an application include:

  • Any allotment within a Special Water Supply Catchment Area
  • Small lot size (under 4000m2)
  • Soils with very low permeability
  • Groundwater quality at risk
  • Development use (i.e., high loading rate due to commercial/industrial activities)
  • Susceptible ecological areas or water bodies nearby
  • Lot characteristics such as slope, location of drains/easements/water courses etc

It may be one factor alone that triggers the need for an LCA or a combination of factors.

Individual landowners or developers (not EPA or Councils) are responsible for engaging a suitably qualified and experienced professional to undertake a LCA for unsewered developments or subdivisions. The Victorian Land Capability Assessment Framework, 2014 provides further guidance.

If you are unsure of whether an LCA is required, please contact Council’s Health Protection Unit on (03) 5232 9400 prior to submitting your application.

Approval to use an OWMS

When you get a final inspection on your septic system, Council will also issue a certificate to use (CTU) an OWMS. There is no additional cost for this permit and you don’t need to apply again.

To obtain a CTU you will need:

  • An inspection by Council's Health Protection Officer - the plumber should contact Council to organise this once the system has been installed.
  • A Certificate of Compliance from the Victorian Building Authority (the plumber will organise this).
  • A commission report (if applicable).
  • An accurate, to scale, as-constructed site plan.
  • An Electrical Certificate (if applicable)
  • A copy of the maintenance service agreement if you’ve installed an Aerated Wastewater Treatment System.

Operating an OWMS

To keep the system working well

✔   use biodegradable soaps and low-phosphorus, low sodium detergents
✔    arrange for regular servicing of treatment plants
✔    keep livestock and vehicles off the system
✔    divert stormwater runoff away from trenches or irrigation areas

    don’t use powerful bleaches, whiteners, nappy soakers, spot removers and disinfectants
x     don’t put chemicals or paint down the drain
x     don’t put pads, tampons or nappies into the system
x     don’t build over the system (driveways, sheds, units etc.)

To reduce sludge building up in the tank

✔   scrape all dishes to remove fats, grease and food scraps before washing
✔    keep food waste out of the system
✔    pump out the tank at least once every 3 years

Avoid overloading the system

✔    space out water use as evenly as possible
✔    wash clothes only when there is a full load
✔    install water conservation fittings
✔    take showers instead of baths

x     avoid doing all the washing on one day
x     avoid using the washing machine and dishwasher at the same time

Maintenance of OWMS

Responsibility for managing and maintaining an OWMS falls with the property owner. An owner of land on which an OWMS operates must provide the occupier with written information regarding the correct operation and maintenance of the system. Persons in control of an OWMS must take all reasonably practicable steps to ensure the system is maintained in good working order and does not pose a risk to human health or the environment.

These steps include:

  • Regular desludging to remove the contents of the system, if applicable
  • Ensuring the integrity of pipes, tanks and storage systems.
  • Repairing and, when required, replacing all the components and fittings of the system.
  • Maintaining the biological and chemical processes integral to the proper functioning of the system.
  • Maintaining the integrity of the land used in connection with the system to ensure access to the system is not impeded.
  • Complying with the system manufacturer's specifications and recommendations.
  • Complying with any relevant council requirements.
  • Monitoring the system for signs of fail.

Persons in control of an OWMS must keep and hold all records of maintenance activities carried out on the system, including any pump-out and service records, for five years after each activity. These records must be made available for inspection upon request by Council.  

Dealing with OWMS failures

It is essential to be vigilant about potential OWMS failures. This means paying attention to key warning signs and taking steps to address the issues, even if this might be contained to your property.

Warning signs of failure may include:

  • the absorption field becoming wet with wastewater pooling on the surface
  • wastewater runoff from the disposal area
  • a smell of effluent near or from the system
  • Shower, basin or toilets draining slowly

If you suspect your system may be failing, please contact a licensed plumber to inspect the system.

The Regulations also require landowners and occupiers to tell their council if their OWMS shows any signs of failure. You will need to explain to a council officer what has or is being done to fix the problem.

If others detect and report issues to council – such as offensive smells - and the owner or occupier has not reported it, a penalty may apply to the owner or occupier.

Decommissioning of a Septic Tank / AWTS

After you have connected to a reticular sewerage or upgraded your old septic or onsite wastewater management system (OWMS), the old septic tank or OWMS must be decommissioned.

The following steps are applicable:

  • Have its contents pumped out by a licensed sewage sludge contractor and the inlet and outlet pipes sealed.
  • Punch a hole in the bottom of the tank, the lids and any parts of the tank walls that sit above ground level so that they collapse into the tank.
  • Fill the tank with clean earth or sand.
  • Any chlorination pits on the sand filter outlets must follow the above process as these may have a direct connection to the stormwater drain.
  • Notify Council of your decommissioning and provide a detailed and to scale site plan of the location.


Decommissioning Notification Form

Tank Size * (required)

I confirm the following * (required)

Colac Otway Shire is committed to full compliance with its obligations under the Privacy and Data Protection Act 2014 (Vic). All personal information collected by Council will be used for processing your septic tank notification and related purposes. We will not disclose your personal information to other third-parties without your consent unless required or authorised by law.

Council's Responsibilities

EPA Permits and Domestic Onsite Wastewater Management Responsibilities

Council is meeting its statutory responsibilities in relation to the assessment, permit and approval process for domestic onsite waste water systems.

Since November 2015, Council has issued 484 permits. Systems installed post 1 July 2016 upon approval would be assessed as EPA compliant.

A calendar year break down of permits is as follow:



















(to 9 August) 42.



A focus of the domestic wastewater management plan activities, is also the auditing and inspections of onsite domestic wastewater systems within declared water supply catchments.

Systems have been assessed and education to property owners and occupiers has been provided. 


Forrest Wastewater Project

Barwon Water has been collaborating with the community, Colac Otway Shire and technical experts to identify a sustainable, long-term, wastewater solution for the town.

Work is continuing to progress to develop a concept design and business case for a wastewater management solution for the township

For more information and updates on the project, please visit: Barwon Water Website - Forrest Wastewater Project


Related Links & Information:

Application form: Install an OWMS (Septic) System Application Form