Waterless toilets

Waterless toilets or ‘dry sanitation’ systems do not use water to treat or transport human excreta. Waterless toilets can have lower environmental impacts than water-efficient toilets and wastewater recycling systems, and much lower impacts than conventional toilets. If appropriately designed, waterless toilets conserve precious water resources and keep effluent and pollutants out of waterways and the general environment. They can also save money on your water bill.

Waterless toilets can reduce the site restrictions, and pollution and nutrient problems, of systems such as septic tanks, and are often preferable to conventional toilets in environmentally fragile or water-scarce areas. For example, in the mid-north coast region of New South Wales, councils recommend householders install waterless toilets rather than conventional septic tank systems.

Photo: Stuart White, ISF

Types of waterless toilets

The many designs of waterless toilets can be divided into 3 main types: continuous composting, batch composting, and self-contained.

Continuous composting toilets

These single-container toilets decompose excrement as it moves slowly through the container and is removed as compost from the end-product chamber. Well-known designs with prefabricated models available for installation have state and territory health department approval in most parts of Australia. They may also be constructed by owner–builders. They may need to be certified by a qualified person.

Single containers are fitted under a bathroom and can easily replicate a flush toilet with little physical adjustment. The container is permanently fitted under the toilet seat, and never has to be fully emptied as the compost can be gradually removed when it reaches the end-product chamber.

A disadvantage of the continuous system is that it may allow fresh material and pathogens (disease-causing organisms) deposited on the top of the pile to contaminate the successfully decomposed end-product at the bottom of the pile.

Another drawback is that, if a problem occurs with the toilet, the system can be out of order until the problem is fixed because there is only one container. Sometimes the pile does not actually move down the slope of the container and can become compacted and very difficult to remove.

Batch composting toilets

Batch composting toilets consist of 2 or more containers that are alternated so that the active container is being used while the pile in the fallow container has time to compost without the addition of fresh excrement and the potential for recontamination.

The full containers in the batch system need to be replaced by an empty container. They must be disconnected from under a toilet seat or the seat moved over a new container. Batch systems can therefore take up more space in the bathroom or under the house.

Some commercially available toilets, including an Australian-made system, have approval for use in most parts of Australia. Some models have removable containers mounted on a turntable beneath the toilet for collecting waste which saves space and simplifies container changeover.

An example of an owner-built batch composting toilet is the ‘wheelie-batch’. Containers are alternated underneath the toilet seat, and a perforated false floor is used to separate and drain off the liquid.

The fixed chamber batch is another example; 2 containers are permanently in place and the seat is moved when the time comes to change containers.

Self-contained composting toilets

Self-contained composting toilets are available for use where a composting chamber cannot be installed beneath the floor, such as an existing on-ground concrete slab. They are usually fitted with a small heater and fan to facilitate waste decomposition, and have the capacity to serve only households with a maximum of 3–4 people.

Photo: Nature Loo

Choosing and installing a design

First, check with your local government or your supplier to confirm that composting toilets can be used in your area. Local regulations vary, but common off-the-shelf units have state health department approval. Owner-built designs are usually cheaper to install and have been used widely for many years, but often have not gone through the required approval process.

There are many types and applications of composting toilets. The published literature and manufacturers’ websites have more information and contacts for commercial units and owner-built designs.

For an off-the-shelf unit, contact several suppliers. Tell them about the building, where the toilet will be located, how many people will be using the toilet and whether it will be on a continuous basis or only occasionally, such as in a holiday house. Ask them to recommend a suitable system for your needs and provide a quote. The cost can vary significantly depending on the design and features. Some suppliers also assist with greywater treatment systems.

Check if the supplier gives after-sales support. Ask if they have any customers with whom you could meet and discuss their experience. The cycle of usage and production of compost or end-product can take a couple of years. It is important to know that all stages of the process work satisfactorily.

Avoid complicated designs. Simple passive systems with minimum moving parts are usually easier and cheaper to build, monitor and maintain. Designs that have more moving parts may require less maintenance if the system is working well. But if there is a problem, the more complicated designs can be more difficult to fix.

All composting toilets require a volume of space under the toilet floor which may necessitate the construction of either a pit or an elevated platform. They generally work best when kept warm so are ideally located on the sunny side of a house.

Maintaining a composting toilet

The composting is technically simple but requires more attention than a flush toilet.

Add some carbon-based material or bulking agent, such as dry leaves or softwood shavings, frequently to the container, preferably daily or with each use. This gives the proper carbon–nitrogen mix, helps aerate the pile and prevents compacting. Some commercial suppliers say this is not necessary for their design if their directions are followed, but the addition of bulking agent helps to produce good compost.

The pile in a composting toilet needs to be well drained. Diverting urine away from the compost can aid the composting process by reducing moisture levels and potential odours. Liquid runoff is often treated in a sealed evapotranspiration trench or a solar evaporating tray. If the liquids have been in contact with faeces, they must be evaporated, sterilised or otherwise treated before they can be recycled as fertiliser. Council or health department regulations require appropriate drainage and disposal for residual moisture.

Vent pipes aerate the pile and can work passively using convection. Install as per manufacturers specifications. Fans are not essential but are often included in off-the-shelf systems to aid ventilation and minimise odours. Check fans occasionally to ensure they are not choked with dust or insects.

Composting toilets do not deal with greywater from showers, kitchen and laundry, so a separate greywater collection and treatment system will be needed refer to Wastewater for more information.

Using the compost

The end product or compost needs to be removed from the container when it is sufficiently decomposed. The frequency of removal depends on the size of container, how often the system is used and local climatic conditions. The minimum ‘fallow’ period should be 6 months. Depending on the design and usage, the container needs to be emptied every 6 months to 3 years.

The composting toilet often does more than the process that occurs in your garden compost heap. Decomposition in the holding tank or container of a toilet takes place through a complex biochemical interaction of factors such as temperature, pH, desiccation and digestion by invertebrates, all taking place over an extended time period.

However, it is safest to assume that the composted end product contains residual disease-causing pathogens. The degree of decomposition and pathogen destruction is sensitive to a range of ambient conditions in the composting mass (such as temperature, moisture, and pH levels) that are difficult for the toilet owner to monitor and control. Therefore, take precautions when using the compost:

• Always use protective clothing such as gloves and mask when handling the composted end-product.
• Use the compost as fertiliser to dig into your garden or dispose of it according to local council regulations.
• If you use the compost in your garden,
  – bury the compost under at least 10cm of soil
  – do not use the compost for cultivating vegetables.

• Booker N (2001). Greywater and blackwater treatment strategies, Environment design guide, TEC 11, Australian Institute of Architects, Melbourne, 1–14.
• Del Porto D and Steinfeld C (1999). The composting toilet system book: a practical guide to choosing, planning and maintaining composting toilet systems, a water-saving, pollution-preventing alternative, Center for Ecological Pollution Prevention, Concord, Massachusetts.
• Van der Ryn S (1999). The toilet papers: recycling waste and conserving water, Chelsea Green Publishing Co, White River Junction, Vermont.
• Water Wally, Composting toilets.
• Windblad U and Simpson-Hebert M (2004). Ecological sanitation, 2nd edn, Stockholm Environment Institute, Stockholm, Sweden.

Learn more

• Review Designing your home to find a wide range of things you should consider in house design
• Explore Renovations and additions for how to update your home to reduce your environmental impact
• Visit Reducing water use for ideas on cutting water demand and use in your home

Authors

Original author: Leonie Crennan

Updated: Geoff Milne 2013