An on-site wastewater management system (OWMS) is generally required for properties that are not connected to TasWater's sewerage network.
An OWMS collects and treats household wastewater, including:
- Greywater from showers, baths, hand basins, kitchens, and laundries.
- Blackwater from toilets.
The system treats wastewater to reduce contaminants and disease-causing microorganisms (pathogens) before it is dispersed into the soil, removed from the site, or, in some cases, reused in accordance with regulatory requirements.
In Tasmania, OWMS installations must meet the minimum requirements of the National Construction Code (NCC) Volume Three, generally through compliance with:
- AS 1546 On-site Domestic Wastewater Treatment Units; and
- AS/NZS 1547 On-site Wastewater Management.
Wastewater can contain pathogens that may cause illness in humans. A properly designed, installed, operated, and maintained wastewater system helps protect public health and the environment by reducing the risk of contamination and exposure.
Poorly designed, installed, or maintained systems can contaminate drinking water supplies, recreational waters, waterways used for food production, and surrounding land. They may also increase the risk of direct human contact with untreated wastewater.
The installation, replacement, or modification of an OWMS is permit plumbing work and generally requires approval from your local council before work begins.
Before undertaking any work, you should refer to the Director's Determination – Categories of Plumbing Work or contact your local council to confirm the approval and permit requirements applicable to your project.
Certificates of Accreditation
Where accreditation is required under the Director's Determination, the treatment unit or system component must hold a current Certificate of Accreditation issued by the Director of Building Control.
All approved on-site wastewater treatment units accredited by the Director of Building Control receive a Certificate of Accreditation which is available on the Building Standards Tasmania website. You can view these certificates to obtain supplier information and technical data. The link below each category allows you to view the certificates categorised by the Standard they were certified to.
Design of wastewater systems
The first step towards a new or upgraded on-site wastewater management system is to engage a licensed wastewater system designer to undertake a land capability assessment (LCA) of your property.
As part of this assessment, soil investigations are undertaken, which may include soil profile inspections, field testing and, where necessary, laboratory analysis, and other site-specific factors are considered, including local environmental conditions, land slope, available land area, drainage characteristics, and planning constraints. Using this information, the designer will determine the most suitable wastewater treatment and disposal system for your property.
The final design will consider factors such as:
- Soil type and permeability
- Site topography and drainage patterns
- Available land area
- Property boundary setbacks
- Watercourses, dams, bores, and other environmental features
- Planning and development requirements
- Current and future land use
Depending on your site's characteristics, you may have several system options available, however, your LCA may also determine that you have no options other than one specific type of system. Your designer can help you understand the advantages, limitations, installation costs, and maintenance requirements of different systems.
The wastewater system design, together with supporting certification and assessment documents, must be submitted to your local council as part of an application for a plumbing permit before installation can commence.
Wastewater management system designs must comply with the minimum requirements specified in the Director's Determination – Director's Specified List, Schedule 2, Part 3.
The Director's Guidelines for On-site Wastewater Management Systems provides additional guidance on the design, installation, operation, and maintenance of wastewater systems and is a useful reference for designers, Environmental Health Officers, installers, and property owners wishing to better understand on-site wastewater management.
Types of wastewater treatment units
Septic tanks
Septic tanks are classed as a primary treatment device. They rely on non-mechanical settling and breakdown of organic material from domestic waste prior to the effluent being conveyed to a land application area system. Septic tanks can also incorporate outlet filtration and/or additional downstream treatment methods to improve the quality of effluent reducing its environmental impact on native soil, this can also extend the life of your system.
A septic tank relies on naturally occurring physical and biological treatment processes. Excessive use of certain chemicals, disinfectants and antibacterial products may adversely affect biological activity within the tank.
An unhealthy septic system produces foul odours and curbs the breakdown of matter. Familiarise yourself with ‘septic-safe’ products for use in the household.
Primary treatment systems may not be suitable for some site and soil conditions, including certain clay soils or highly permeable sandy soils. Your licensed designer will be able to provide advice on whether this system is an option for your property.
Septic tanks require less maintenance than systems that rely on mechanical processes, but still require pumping out every few years to maintain settling volume.
See list of accredited septic tanks for more information.
Waterless composting toilets
A waterless composting toilet (WCT) treats waste using a composting process requiring little to no additional water. The end product is a stabilised organic material with significantly reduced pathogen levels when the composting process operates correctly.
The output is a less offensive product that can either be removed from site or buried on-site in a manner allowed by the Australian Standard AS/NZS 1546.2 or as conditioned on your plumbing permit. These systems can be a great solution for off-grid homes or as a sustainability measure where water conservation is a focus.
Restrictions apply under the NCC Housing Provisions, relating to the installation of these systems in buildings. Your licensed designer can provide recommendations if this system would be suitable for your property.
Removable pan type WCTs are not to be installed within 2m of a building containing habitable rooms under the NCC Deemed-to-Satisfy provisions.
Waterless composting toilets accredited under the Tasmanian plumbing framework are intended for installation in buildings and are generally not approved for use in registrable vehicles such as caravans or other trailer-based dwellings.
See list of accredited Waterless Composting Toilet systems for more information.
Secondary treatment systems
A secondary treatment system (STS) collects all domestic wastewater which is then passed through several settling and filtration stages to meet a specific treated effluent quality standard using either passive or mechanical processes, prior to being distributed to the land application system. Depending on treatment performance, accreditation conditions and local approval requirements, disinfected secondary treated effluent may be suitable for alternative land application methods such as surface irrigation or spray irrigation.
The improved effluent quality provides greater flexibility for land application design. The requirement to install an STS is determined by your licensed designer based on compatibility with your property and Local Government provisions. Your licensed designer will be able to offer options for system types during the consultation and design phase.
Most accredited secondary treatment systems require ongoing servicing under a maintenance contract. Servicing frequencies vary between systems but commonly occur on a quarterly basis in accordance with the Certificate of Accreditation.
See list of accredited Secondary Treatment systems for more information.
Domestic greywater treatment systems
A greywater treatment system isolates greywater from sanitary fixtures such as showers, baths, and basins (excluding toilets) and disinfects the water for short-term storage prior to land application. Subject to the conditions of accreditation and approval, treated greywater may be reused for purposes such as toilet flushing, subsurface irrigation and, where specifically approved, clothes washing. Due to the hazardous pathogens found in greywater, the storage of untreated greywater is not permitted.
Treated greywater effluent is not suitable for irrigating vegetables, fruit, or any other produce for consumption.
Land application systems
Once domestic wastewater has been treated by an OWMS it is transferred to a Land Application System (LAS) where it is dispersed to land where further treatment occurs through soil processes, evapotranspiration and plant uptake.
Depending on the level of treatment, effluent can be distributed via various land application methods including absorption trenches, transpiration beds, subsurface irrigation, surface irrigation, or incorporate other proprietary systems.
Factors that can influence the design include:
- Soil structure
- Site slope
- Available land area
- The water table
- Proximity to waterways or neighbouring properties
- Local Council specific requirements
- Limiting layers (rock etc.)
There are a range of conventional methods for effluent distribution and new technologies that can further improve effluent quality prior to dispersal into the land. Your licensed designer can discuss options with you based on compatibility with your property.
Any installation, alteration, repair, replacement, or upgrade of an on-site wastewater management system (OWMS), including a land application system (LAS), requires a plumbing permit and must be carried out by a licensed plumber.
Greywater
Greywater is often perceived as relatively clean because it comes from showers, baths, hand basins, laundries, and kitchens rather than toilets. However, greywater can contain a wide range of contaminants, including human pathogens, food waste, fats, oils, grease, detergents, chemicals, hair, skin particles, and organic matter. When stored or managed incorrectly, greywater can rapidly deteriorate, producing unpleasant odours and allowing bacteria and other microorganisms to multiply. For this reason, untreated greywater should not be considered safe, and it requires appropriate treatment and disposal to protect human health and the environment.
It is generally disposed of through your wastewater systems however, reuse of greywater can be considered using either a treatment/recycling system, diversion system, or by manually collecting it for garden use.
Manual greywater reuse
Owners may manually collect greywater from baths, showers or similar fixtures and immediately apply it directly to land provided this does not create a nuisance, health risk or environmental harm. However, this can only be done in conjunction with a fully approved wastewater management system and is not an appropriate solution in isolation. It is critical that manually collected greywater is not stored for more than 24 hours prior to being distributed to the land.
Greywater diversion devices can be manually controlled to send greywater to garden areas however; they must only ever be installed inline of an approved disposal system. The installation of such systems must only be done under an approved plumbing permit.
Incinerator toilets
There are several ‘Incinerator’ style toilets available on the market for the purpose of disposing of faecal waste. These systems rely on an incineration process to destroy any pathogens and reduce the remaining waste product to a small volume of ash with minimal public health risk when managed correctly.
Incinerator toilets require no additional water for the disposal process and are desirable for situations where water conservation is a focus.
The absence of a waste output means the Director of Building Control does not accredit these products and they can be installed in Tasmania provided they meet the required electrical and gas certification requirements and any other government regulations. An important note however, as required by the NCC deemed-to-satisfy provisions, incinerator toilets are not to be installed within 2m of a building containing habitable rooms. This limitation generally prevents the installation of incinerator toilets within dwellings as a Deemed-to-Satisfy solution. Installation within a dwelling may require a Performance Solution.
The remaining wastewater i.e., kitchen, laundry or sanitary fixtures must be treated and disposed of in accordance with the NCC through an accredited wastewater treatment system.
Maintenance of your on-site wastewater management system
As the owner, or occupier of a property with an on-site wastewater management system (OWMS), you are responsible for ensuring the system is properly maintained and continues to operate as approved. Regular maintenance is essential to protect your family's health, prevent environmental contamination, and maximise the life of your wastewater system.
Septic tanks (primary treatment systems)
Septic tanks require periodic desludging to remove the layer of accumulated sludge and scum that builds up over time. While the required frequency may be specified in your plumbing permit or by regulatory requirements, septic tanks should generally be desludged every three years to maintain effective performance.
When sludge accumulates beyond acceptable levels, the septic tank's treatment and storage capacity is reduced. This can allow poorly treated effluent and solids to leave the tank, potentially causing blockages, overloading disposal areas, and premature failure of the land application system.
Only a controlled waste transport business registered with the Tasmanian Environment Protection Authority (EPA Tasmania) can remove and transport septic tank waste.
Secondary treatment systems
Secondary treatment systems require a higher level of ongoing maintenance to ensure they continue producing effluent to the required quality standard.
When a secondary treatment system is installed, the owner must enter into a statutory maintenance contract with a licensed plumber in accordance with the conditions of the system's Certificate of Accreditation. Regular servicing helps identify faults early, confirms the system is operating correctly, and ensures the required effluent quality is being achieved.
Service reports are generally required to be provided to the relevant local council in accordance with plumbing permit conditions.
Maintenance records
Owners must retain servicing and maintenance records for their wastewater system. These records may be required by council, future property owners, or service providers and must be kept for a minimum of 10 years under the Building Act 2016.
Why maintenance matters
An on-site wastewater system is not a 'set and forget' installation. Routine servicing, inspections, and desludging are essential to maintaining system performance and preventing costly failures. A well-maintained system protects public health, groundwater, waterways, and your property while helping to avoid expensive repairs or replacement of disposal areas.
For further information, refer to the Director's Determination – Accreditation and Maintenance of Plumbing Installations and the Director's Guidelines for On-site Wastewater Management Systems.