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Composting toilets can be used where there is no mains sewer connection or in some circumstances to reduce demand on the mains sewer.
On this page:
- how they work
- statutory requirements
- requirements of composting toilet system
- deciding to install a composting toilet
Also see types of composting toilets.
How composting toilets work
Flushing toilets account for approximately 20% of domestic water use. Composting (or waterless) toilets eliminate the need for flushing water.
A composting toilet breaks down human waste and other added organic material by an aerobic process in the same way that garden compost is made. The end product should be an odourless, soil-like humus that can be buried on-site.
For the composting to occur, the moisture content in a composting toilet must be minimal. This generally requires separating out the urine by evaporation or a separate collection system.
The urine can then be disposed of by:
- a septic tank or other on-site blackwater treatment system
- a rock filled soakaway/soakpit
- a storage tank – it can be used as a fertiliser for citrus trees.
Approval from the local council for the proposed disposal method must be obtained.
A composting toilet cannot be used in urban areas where a mains sewerage system is available. Under the Building Code, if a mains sewerage connection is available, toilets must be connected to it unless the building consent authority provides a waiver.
The standard requirements of waterless composting toilets for residential use are covered by AS/NZS 1546.2:2008 On-site domestic wastewater treatment units - Waterless composting toilets.
Waterless composting toilets that are constructed separately from the house come within the description of a building under the Building Act 2004.
The plumbing installation within the house must comply with the requirements of NZBC clauses G12 Water supplies and G13 Foul water.
Be aware that some local authorities also have their own requirements and restrictions around composting toilets that you must comply with.
Requirements of composting toilet system
Composting toilets must contain and act on pathogens. They must:
- meet good sanitation and public health requirements
- keep human contact with effluent to a minimum
- prevent contact with disease carriers, such as flies
- produce no offensive smells
- end with an inoffensive product with low concentrations of harmful bacteria.
In addition, they:
- can usually only be installed where there is no available public sewer connection
- require continuous extract ventilation
- may require a separate urine disposal system
- must have an alternative means of disposal for maintenance or repair of the system.
Deciding to install a composting toilet
They require a commitment to monitor and maintain the system, which involves:
- changing the full bins with batch systems
- removing the compost at regular intervals from continuous systems
- adding soil, burying or disposing of the compost
- cleaning the system as required by the manufacturer.
If a composting toilet is not properly maintained and monitored, the end product may not be properly composted, which means:
- removal and cleaning may be unpleasant
- there may be a health risk
- there may be odours.
Updated: 12 December 2022