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    About Greywater

    Waterless Composting Toilets and grey-water systems go hand in hand. A waterless composting toilet will manage all human excreta, however, when it comes to household waste, you still need to look after the wastewater that comes from your kitchen, sinks, basins, showers, bath-tubs, washing machines, dishwashers etc. All this comes under the category of grey-water.

    Firstly, what is grey-water?

    Grey-water is essentially all household wastewater from kitchen sinks, dishwashers, laundry tubs, washing machines, baths, tubs and basins. Usually, a building consent is required for the collection and use of grey-water. It’s important to remember that grey-water may contain certain contaminants and therefore is not suitable for cooking, bathing or drinking.

    Water which may contain feacal matter, such as water which comes from your toilet or bidet is known as black-water. This water cannot be reused anywhere in the house and must go into either a septic system, another form of treatment or mains sewage. Our recommendation is (obviously) to eliminate the need for black-water treatment through the use of a waterless composting toilet system.

    Why divert grey-water from black-water?

    The simple reason to argue for separate treatment of grey-water is that water is a valuable resource. Grey-water, when treated properly can be an asset and can be used on-sight as part of irrigation schemes. This re-use of water allows for more efficient homes which consume fewer resources and therefore have a lower negative environmental impact.

    Re-Using grey-water

    There are many reasons to re-use your grey water. These can include water savings, reduced water and wastewater charges (saving you money) and overall helping to reduce demand for water supplies in your area.

    Ultimately, there are different levels of grey-water re-use. This can include use of water from sinks to flushing toilets (not required in our waterless composting toilets, but relevant in micro-flush systems such as the sun-mar micro flush), washing of clothes, and also irrigation in the garden.

    It’s important to note here that due to increased risk of contamination, grey-water from the kitchen sink is also deemed as unfit for re-use and requires additional treatment.
    When storing grey-water for re-use, it’s essential that it’s kept well stored and separate from the freshwater supplies. Grey-water must be clearly labelled to ensure that nobody drinks from this supply.

    The most common re-use of grey water is irrigation of gardens. This allows users to maintain a lush and green garden all year round simply through using water that would otherwise be going down the drain. On average, this allows households to reduce their yearly water use by up to 50% depending on the size of their garden, significantly reducing expense in areas with metered water.

    How a Grey-water system works

    There are many different types of greywater treatment systems on the market and ultimately it comes down to the user to research and specify the best solution for their particular application.
    In most instances, grey-water treatment begins with water from basins, baths, showers etc. being piped into a surge tank. This enables the grey water to be briefly held before being discharged to either a direct irrigation system or an additional treatment system. This can occur either through gravity, or use of a pump.

    It’s important to note that the surge tank must be emptied each time the grey water is dispersed and that no grey water should be allowed to sit for extended periods of time in the tank. Should this happen, undesirable bacteriological and viral growth may be allowed to occur in the tank. This should be avoided at all costs.

    The surge tank for the grey water should be vented with a trapped overflow. And discharge must lead directly into the sewer or to an on-site discharge area. It must be sealed and vermin proof.

    Treatment of Grey-water

    Again, there are several options when it comes to the treatment of grey-water and the specific option you choose should be specifically suited to your unique application. Options for treatment may include filtering, settlement of solids, flotation, and operation of lighter solids, anaerobic or aerobic digestion, chemical or UV disinfection. Once set-up, grey water collection and re-use is hassle free and low maintenance, although they do tend to require some level of attention. Greywater filters, for example, will require periodic replacement and any solids that build upon tanks must be removed regularly.

    Purchase ready-made grey-water systems for your home.

    In New Zealand, commercially manufactured grey-water systems that meet the requirements for treatment and reuse of water are available. These units are typically comprised of a plastic gully with a grating, a submersible pump which automatically moves the grey-water to the irrigation system, a manual or remote over-ride switch which allows for grey-water to be diverted to the sewer if required and a partially self-cleaning filter.

    At this time, WCTNZ has no specific recommendations for grey-water treatment options, as each site has its unique set of challenges and therefore is suited to different systems.
    Pairing a suitable grey-water system with a waterless composting toilet is an ideal way to maximize the use of your resources on site, and build resilience, efficiency, and environmental consciousness into your home.

    How do I find the grey-water system that’s right for my property and that will compliment my composting toilet?

    To ensure that you correctly match your grey-water system to your composting toilet, we recommend speaking with a professional who can help you design your entire system. Please find below the name and contact details of recommended organizations who know our composting systems and will help you to spec complementary grey-water options.

    North Island / NZ

    • Dylan Timney /

    South Island / NZ

    • Jeff Jain /