Blog: when and why you need a wastewater report: rules for new builds, granny flats, and extensions in NSW

If you’re building in regional or semi-rural New South Wales — whether it’s a new home, a granny flat, or an upgrade to an existing property — chances are you’ll need a wastewater report. Councils take on-site wastewater management seriously because poor design can affect land usability, groundwater, neighbours and the environment.

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But when exactly is a report required? What do councils expect? 

Let’s break it down.

When a Wastewater Report Is Required

Most councils across NSW will ask for a wastewater report (or “On-Site Wastewater Management”) in these situations:

• New builds on land not connected to mains sewer.

• Secondary dwellings / granny flats, or alterations where an extra bedrooms or bathrooms add additional wastewater load.

• Property upgrades that involve additional plumbing fixtures (e.g. adding a new bathroom, laundry, or kitchen).

• Subdivision of land where new lots will require their own on-site wastewater solutions.

• Replacement or upgrade of an existing septic system that no longer complies or has failed.

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👉 Rule of thumb: If your project changes how much wastewater a property will generate, or if the land has no access to mains sewer, a wastewater report will almost always be required.

What Councils Expect in a Wastewater Report

While requirements vary by council, most reports must address:

• Site and soil assessment – soil type, slope, drainage, water table, environmental constraints.

• System selection – recommended type of on-site wastewater system (septic, aerated wastewater treatment system, etc.)

• Design details – disposal area sizing, setbacks from boundaries, dwellings and watercourses.

• Environmental protection – how the design avoids contamination of water or land.

• Operation and maintenance – how the system will be serviced over time.

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Council Timelines and Approval Process

• Lodgement – The wastewater report is usually submitted as part of the Development Application (DA) or Complying Development Certificate (CDC).

• Assessment – Council’s environmental health officers review the report for compliance with NSW guidelines (the key one being Environment & Health Protection Guidelines – On-Site Sewage Management for Single Households).

• Approval / conditions – When the report meets requirements, approval will be issued with conditions (e.g. system type, installation standards, maintenance schedule).

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Timelines vary, but typically wastewater reports are reviewed within 2–4 weeks as part of the broader DA process.

What Happens If You Skip It

• Delays: Your DA or CDC may be refused or delayed until a report is provided.

• Compliance notices: Installing or upgrading a system without approval can lead to orders from council to stop work or remove the system.

• Penalties: Councils can issue fines, and in serious cases, take legal action.

• Cost blowouts: Fixing non-compliant systems is far more expensive than getting the right report and approval up-front.

Council Comparisons

Here’s a snapshot of what some local councils require:

• Shoalhaven City Council – Requires a wastewater report for all unsewered development, with strict setbacks from waterways and flood-prone land.

• Wingecarribee Shire (Southern Highlands) – Strong focus on WaterNSW catchment compliance.

• Goulburn Mulwaree Council – Requires detailed wastewater management plans for secondary dwellings, even when upgrading existing systems.

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While the principles are similar, each council has its own nuances — which is why a consultant familiar with local rules can save you a lot of hassle.

Key Takeaways

• A wastewater report is required for new builds, granny flats and property upgrades on unsewered land.

• Councils want to see that your design is safe, sustainable and compliant.

• Submitting a clear, compliant report upfront avoids costly delays and penalties.

• Requirements vary across councils, so local expertise matters​

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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.