If you’re planning a new build, a granny flat, or upgrading an existing home in the Southern NSW, one of the key questions to consider is how you’ll manage your household wastewater.

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You'll often hear terms like greywater and blackwater, but what do they mean? And which type of system is best suited to your land, climate, and council requirements?

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This guide breaks down the differences, costs, environmental impacts and compliance factors to help you make an informed choice.

 

Greywater vs Blackwater: The Basics

• Greywater

  • Comes from showers, baths, hand basins, washing machines, and laundries.

  • Relatively low in pathogens, but can still contain soaps, detergents, and small contaminants.

  • Can often be treated and reused for irrigation or toilet flushing.

• Blackwater

  • Comes from toilets and sometimes kitchens.

  • Contains higher levels of pathogens, nutrients and organic matter.

  • Requires treatment through a septic tank, aerated wastewater treatment system (AWTS), or advanced on-site wastewater system.

 

Costs and Benefits

Greywater systems

• Upfront cost: Generally lower than full blackwater treatment systems.

• Ongoing costs: Minimal if used for irrigation, but may require maintenance to avoid blockages.

• Benefit: Reduces demand on mains water (great for gardens and lawns in places like Moss Vale, Berry, and Milton).

Blackwater systems

• Upfront cost: Higher, due to treatment tanks and disposal areas.

• Ongoing costs: Regular servicing and possible effluent testing required by councils.

• Benefit: Safely manages all wastewater on site; required where sewer is unavailable.

 

Environmental Impact

• Greywater reuse can significantly reduce potable water use, which is valuable in drier areas like Goulburn and Braidwood, where rainfall is lower and soils can be shallow.

• Blackwater systems protect public health by safely treating sewage, but they require more energy and maintenance.

• Combined approaches (greywater reuse + blackwater treatment) can provide a sustainable outcome, especially in wetter, high-rainfall areas like Nowra or Kangaroo Valley, where soils may become waterlogged without careful system design.

 

Council Compliance

Local councils across the South Coast, Southern Highlands and Southern Tablelands have specific rules for wastewater management:

• Shoalhaven City Council (South Coast NSW): Typically requires a full wastewater assessment for new builds, focusing on setbacks from waterways and flood-prone land.

• Wingecarribee Shire Council (Southern Highlands): Careful attention to WaterNSW Catchment compliance.

• Goulburn Mulwaree Council (Southern Tablelands): Strong compliance focus on managing increased wastewater loads from granny flats and secondary dwellings.

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Key takeaway: councils don’t allow untreated greywater or blackwater disposal. A wastewater consultant can design a system that balances sustainability, compliance, and cost.

 

Local Conditions Matter

Choosing between greywater and blackwater solutions isn’t one-size-fits-all. Local conditions in Southern NSW play a big role:

• Soil types: Sandy soils on the South Coast may allow for more irrigation options, while heavier clays in the Highlands need larger disposal areas.

• Rainfall: High rainfall zones (Nowra, Kangaroo Valley) require careful design to avoid waterlogging, while drier areas (Goulburn, Tarago) benefit from greywater reuse.

• Land slope: Steeper blocks in places like Bundanoon or Milton may need pumped irrigation systems or specially designed effluent trenches.

 

Which Is Right for You?

• If you’re aiming for sustainability: Greywater reuse is an excellent way to cut down on water bills and support landscaping.

• If you’re building on unsewered land: A blackwater treatment system (septic or AWTS) will be essential for compliance.

• For many properties: A combined system offers the best balance of compliance, sustainability, and cost effectiveness.

 

Final Thoughts

Deciding between greywater and blackwater systems depends on your property’s location, soil, rainfall, slope, and council requirements. A professional wastewater assessment will give you a clear picture of what’s possible — and what will be approved.

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Get in touch today at info@southernwastewater.com.au to discuss your on-site wastewater assessment needs. We're here to help.