Composting toilets are popular among off-grid and sustainable living advocates on rural properties in the Hastings hinterland. On the Comboyne Plateau, in the Wauchope hinterland, and on King Creek-Beechwood rural blocks, they’re increasingly seen as an alternative to conventional septic, or a companion to a greywater system. But composting toilets in NSW exist within a regulatory framework that many property owners don’t fully understand before installation.
Quick answer (BLUF)
Composting toilets are legal in NSW for rural properties not connected to sewer, but they require PMHC OSSM approval as part of a combined on-site sewage management system. A composting toilet handles the blackwater/solids stream, but does not manage greywater, you still need an approved greywater management system for kitchen, bathroom, and laundry waste. Total compliance cost is comparable to a conventional system.
What a composting toilet actually does
A composting toilet manages human waste (faeces and urine) without water-based flushing. The waste is collected in a composting chamber where:
- Aerobic biological activity (with managed airflow) decomposes the faeces
- Evaporation reduces moisture content
- The resulting compost is stabilised and pathogen-reduced (but not pathogen-free)
The end product, compost, can be applied to non-edible garden areas, but in NSW must meet the standards for treated human waste before land application. This is a condition of PMHC’s approval.
What a composting toilet does not do:
- Manage greywater (shower, bath, sink, laundry)
- Manage kitchen waste water
- Treat urine if it’s not managed within the composting system
- Eliminate the need for any on-site sewage management system
The NSW regulatory framework
In NSW, composting toilets fall under the same On-Site Sewage Management (OSSM) framework as conventional septic and AWTS systems. They are regulated under the Local Government Act 1993 and require PMHC OSSM approval.
The NSW Department of Health publishes approved composting toilet systems. Only products on the approved list can be installed in NSW. Currently approved categories include:
- Self-contained composting toilets (compact units with internal composting chamber, suitable for low-use situations like cabins, weekenders)
- Central composting toilet systems (separate composting unit, often in a separate structure or ground floor, with seat/pedestal units above, more suitable for full-time residential use)
The composting toilet approval is combined with a greywater management system approval as part of a single OSSM application. PMHC will not approve a composting toilet in isolation, you must also have an approved greywater system.
The greywater system: the part most people miss
This is where composting toilet installations often go wrong. Property owners install a composting toilet assuming it eliminates the need for any treatment system, then find themselves in breach of their OSSM approval (or unable to get one) because greywater is flowing untreated.
A typical household generates:
- Toilet waste (blackwater): approximately 35-45% of total wastewater volume
- Bathroom (showers, handwashing): approximately 35-40%
- Laundry: approximately 15-20%
- Kitchen sink: approximately 5-10%
With a composting toilet handling the blackwater, you still need to manage 55-65% of your household wastewater through an approved greywater system. The greywater system typically involves:
- A treatment unit (filtration, UV, or combined system)
- An absorption area for the treated greywater (trenches or drip irrigation)
- PMHC approval, setback compliance, and site assessment, essentially the same requirements as a conventional system, but for a reduced flow volume
When composting toilets make sense on Hastings properties
Constrained sites with limited absorption area: Because the blackwater is handled in the composting unit (no liquid discharge), the absorption area only needs to manage greywater, a significantly smaller volume. This can be the difference between being able to achieve compliant setbacks on a constrained lot and not.
Water-scarce properties: Composting toilets use no flushing water (self-contained) or very little (some central systems use a small water flush into a composting chamber). On properties with limited rainwater storage, this is meaningful water conservation.
Properties with very tight septic system land constraints: On some smaller lots in the Comboyne and Beechwood areas where achieving the full setback requirements for a conventional system is very difficult, a composting toilet plus compact greywater system may be the only viable OSSM solution.
Practical realities: what to know before you commit
Self-contained units are not suitable for full-time residential use on their own: Small self-contained composting toilets are designed for low and intermittent use. A full-time household of 4 will overwhelm a self-contained unit’s composting capacity. Full-time residential use requires a central system with adequate composting capacity.
Management is ongoing: A composting toilet requires regular maintenance, turning/aeration of the compost, moisture management, occasional bulking material addition (wood shavings or similar). It’s more hands-on than a flush toilet.
Insects: Without careful management (sealed lid, appropriate airflow, correct carbon/nitrogen ratio), composting toilets can attract flies. This is manageable but requires attention.
End product management: The composted output must be handled appropriately under NSW requirements. It cannot go in green waste bins. Most PMHC approvals specify how the end product must be treated and where it can be applied.
Cost: A good-quality central composting toilet system (e.g., Clivus Multrum, Nature’s Head, BioLet) costs $3,000 to $10,000 for the unit. Add installation, PMHC approval, and a greywater system, and total costs are comparable to a conventional septic.
FAQs
Can I install a composting toilet without Council approval?
No. In NSW, composting toilets require PMHC OSSM approval as part of a combined system. Operating an unapproved composting toilet is a breach of the Local Government Act 1993 and PMHC can require removal and compliant installation.
Can I retrofit a composting toilet to an existing septic system?
Yes, in some cases. If your existing septic system handles both toilet waste and greywater, you can potentially retrofit by diverting toilet waste to a composting unit and reducing the load on the septic (now handling only greywater). This requires a modification to your OSSM approval, contact PMHC before making any plumbing changes.
Do composting toilets smell?
A properly functioning composting toilet has minimal odour. The composting process is aerobic, it produces CO₂ and water vapour, not the hydrogen sulphide of anaerobic decomposition. Odour problems typically indicate insufficient airflow, a waterlogged composting chamber, or incorrect C/N ratio.
Are composting toilets suitable for Airbnb or holiday rental properties?
With caveats. Guests unfamiliar with composting toilets may not manage them correctly. Clear instructions and a unit designed for intermittent high-use are essential. Some hosts find guests have a negative experience and leave poor reviews.