Wastewater is used water from houses, businesses, industry, and agriculture. It also includes any stormwater or groundwater that enters the sewer system. 

Wastewater can contain physical, chemical and biological pollutants. It goes through the sewerage system or is treated onsite. The main types of wastewater are:

  • greywater – from showers, baths, hand basins, washing machines, laundry troughs and kitchens
  • blackwater – for example, toilet waste
  • sewage – a combination of greywater, blackwater and trade waste
  • industrial wastewater – includes all wastewater waste except sewage. Industrial wastewater varies in quality and quantity depending on the industry type or business size.

How wastewater can impact human health and the environment

Wastewater can contain microorganisms, bacteria and viruses that can cause disease. This can include eye and nose infections or gastroenteritis (gastro or upset stomach). Wastewater can also contain pollutants. These can impact water quality, harm plants and animals and present risks to human health. 

Pollutants include:

  • suspended solids or sediment – soil, sand and other particles can build up in waterways
  • microorganisms – can spread disease (for example, harmful bacteria, virus, protozoa and helminth)
  • chemicals and heavy metals – in industrial waste and naturally present in the environment. These can be harmful in large amounts.
  • nutrients (Nitrogen and Phosphorus) – wastewater high in nutrients entering a water body can cause harmful algal blooms that impact water quality and cause fish kills. 
  • water with too high or too low pH also presents a risk to the environment (biota) and human health when there is close human contact.

All these can impact water quality, harm plants and animals that depend on water and present risks to human health.

How to control risks from wastewater

Controlling the risks from wastewater should happen from the wastewater catchment, through to treatment, disposal and reuse.


Wastewater is collected in different ways. This will depend on the quality and quantity of wastewater, site conditions and other considerations. 

Collection includes:

  • the sewerage system, that flows into a wastewater treatment facility
  • collection and treatment onsite
  • temporary storage before transfer to a licenced facility  for treatment.


Wastewater can be treated in different ways. This depends on the quality and quantity of wastewater, site conditions and what the treated wastewater will be used for:

  • Wastewater  treated to primary quality can only be disposed below ground. For example soil absorption trenches, mounds and evapo-transpiration beds or trenches
  • Wastewater treated to secondary quality can also be dispersed to land via subsurface irrigation
  • Greywater treated to advanced-secondary quality can be used at home for flushing toilets and in washing machines. It can also be used for surface and subsurface irrigation.

Wastewater treatment:

  • For wastewater from domestic and smaller-scale commercial properties in an unsewered area, an onsite wastewater management system is used. There are requirements for owners and occupiers of land with an onsite wastewater management system that are regulated by councils. Refer to the Code of practice – onsite wastewater management (publication 891).
  • For a larger wastewater catchment, use appropriate treatment technologies for the quality and quantity of wastewater. This will depend on the required quality target for disposal and reuse. 

Disposal and reuse

Wastewater treated to the required quality can be disposed to land, discharged to a waterway or coastal/ocean outfall, or reused onsite or offsite:

Wastewater and the general environmental duty  

The general environmental duty (GED) is central to the Environment Protection Act 2017. It applies to all Victorians. The GED requires you to reduce the risk of harm to the environment or human health from your activities.

There are many ways you can do this. For example:

  • Keep your onsite wastewater management system (such as a septic tank system) in good working order
  • Manage the risk when disposing or reusing appropriately treated wastewater to the land.

Read more about wastewater

Reviewed 19 December 2022